Sea-islands type composite fiber having excellent moisture absorbability, false twist yarn, and fiber structure

ABSTRACT

A sea-islands type composite fiber includes an island component that is a polymer having moisture absorbability; a ratio (T/R) of a thickness T of an outermost layer to a diameter R of the fiber in a transverse cross section of the fiber of 0.05 to 0.25; and a moisture absorption rate difference (ΔMR) after a hot water treatment of 2.0 to 10.0%, wherein the thickness of an outermost layer is a difference between a radius of the fiber and a radius of a circumscribed circle formed by connecting apexes of the island components disposed in an outermost circle, and represents a thickness of a sea component in the outermost layer.

TECHNICAL FIELD

This disclosure relates to a sea-islands type composite fiber including an island component that is a polymer having moisture absorbability, and has excellent moisture absorbability. More specifically, the disclosure relates to a sea-islands type composite fiber that does not undergo cracks of a sea component upon volume expansion of a polymer having moisture absorbability that serves as an island component during a hot water treatment such as a dyeing treatment, rarely undergoes generation of dyeing specks and/or fluffs when the composite fiber is formed into a fiber structure such as a woven fabric or a knitted fabric, has excellent quality, is reduced in elution of the polymer having moisture absorbability, also has excellent moisture absorbability even after a hot water treatment such as a dyeing treatment, also has a dry touch inherent to a polyester fiber when the sea component is polyester, and thus can be suitably used for clothing applications.

BACKGROUND

Polyester fibers are inexpensive, excellent in mechanical properties and dry touch and, therefore, are used in a wide range of applications. However, since they have poor moisture absorbability, they have problems to be solved from the viewpoint of wearing comfort such as generation of a stuffy feeling at high humidity in the summer and generation of static electricity at low humidity in the winter.

So far, various proposals have been made on methods of imparting moisture absorbability to polyester fibers to solve the above-mentioned drawbacks. Examples of the common method of imparting moisture absorbability include copolymerization of a hydrophilic compound and addition of a hydrophilic compound to a polyester. Examples of the hydrophilic compound include polyethylene glycol.

For example, Japanese Patent Laid-open Publication No. 2006-104379 proposes a fiber including a polyester copolymerized with polyethylene glycol as a moisture absorbing polymer. In that proposal, the moisture absorbing polymer is singly formed into a fiber to impart moisture absorbability to a polyester fiber.

Japanese Patent Laid-open Publication No. 2001-172374 proposes a core-sheath type composite fiber in which a polyester copolymerized with polyethylene glycol is disposed as a core and polyethylene terephthalate is disposed as a sheath. In that proposal, moisture absorbability is imparted to the polyester fiber by disposing a moisture absorbing polymer on the core.

Japanese Patent Laid-open Publication No. 8-198954 proposes a sea-islands type composite fiber in which a polyester copolymerized with polyethylene glycol is disposed as an island and polyethylene terephthalate is disposed as a sea. In that proposal, moisture absorbability is imparted to the polyester fiber by disposing a moisture absorbing polymer on the island.

However, the method described in Japanese Patent Laid-open Publication No. 2006-104379 has a problem that the moisture absorbing polymer is exposed on the whole fiber surface, and thus polyethylene glycol, which is a copolymerization component of the moisture absorbing polymer, elutes during a hot water treatment such as a dyeing treatment, resulting in reduced moisture absorbability after the hot water treatment.

The method described in Japanese Patent Laid-open Publication No. 2001-172374 has a problem that the sheath component cracks upon the volume expansion of the moisture absorbing polymer of the core component during a hot water treatment such as a dyeing treatment, and dyeing specks and/or fluffs are generated, resulting in reduced quality. Furthermore, the method has a problem that the moisture absorbing polymer of the core component elutes from the cracked portion of the sheath component as a starting point, resulting in reduced moisture absorbability after the hot water treatment.

The method described in Japanese Patent Laid-open Publication No. 8-198954 has a problem that the sea component cracks upon the volume expansion of the moisture absorbing polymer of the island component during a hot water treatment such as a dyeing treatment due to the small thickness of the sea component of the outermost layer relative to the fiber diameter in the transverse cross section of the fiber, and dyeing specks and/or fluffs are generated, resulting in the reduced quality, as in the method described in Japanese Patent Laid-open Publication No. 2001-172374. Furthermore, the method has a problem that the moisture absorbing polymer of the island component elutes from the cracked portion of the sea component as a starting point, resulting in reduced moisture absorbability after the hot water treatment.

It could therefore be helpful to provide a sea-islands type composite fiber that rarely undergoes generation of dyeing specks and/or fluffs when the composite fiber is formed into a fiber structure such as a woven fabric or a knitted fabric, has excellent quality, has excellent moisture absorbability even after a hot water treatment such as a dyeing treatment, also has dry touch inherent to a polyester fiber when the sea component is polyester, and can be suitably used for clothing applications.

SUMMARY

We thus provide a sea-islands type composite fiber including: an island component that is a polymer having moisture absorbability; a ratio (T/R) of a thickness T of an outermost layer to a diameter R of the fiber in a transverse cross section of the fiber of 0.05 to 0.25; and a moisture absorption rate difference (ΔMR) after a hot water treatment of 2.0 to 10.0%. The thickness of an outermost layer is a difference between a radius of the fiber and a radius of a circumscribed circle formed by connecting an apex of the island component disposed in an outermost circle, and represents a thickness of a sea component in the outermost layer.

The thickness T of an outermost layer is preferably 500 to 3,000 nm, and the diameter r of the island component in the transverse cross section of the fiber is preferably 10 to 5,000 nm.

Further, it is preferable that the island component be disposed to form 2 to 100 circles in the transverse cross section of the fiber, a ratio (r1/r2) of a diameter r1 of the island component disposed to pass through a center of the transverse cross section of the fiber to a diameter r2 of other island components be 1.1 to 10.0, the shape of the center side of the island component disposed in the outermost circle in the transverse cross section of the fiber be non-circular, and a composite ratio (a weight ratio) of the sea component/the island component be 50/50 to 90/10.

The polymer having moisture absorbability of the island component is preferably at least one polymer selected from the group consisting of a polyetherester, a polyether amide, and a polyetherester amide containing a polyether as a copolymerization component. The polyether is preferably at least one polyether selected from the group consisting of polyethylene glycol, polypropylene glycol, and polybutylene glycol, and it is preferable that the polyether have a number average molecular weight of 2,000 to 30,000 g/mol, and the copolymerization ratio of the polyether be 10 to 60% by weight.

It is preferable that the polyetherester contain an aromatic dicarboxylic acid and an aliphatic diol as main components, and contain the polyether as a copolymerization component, or contain the polyether and an alkylene oxide adduct of a bisphenol represented by General Formula (1) below as a copolymerization component. The aliphatic diol is preferably 1,4-butanediol.

wherein m and n are integers of 2 to 20 and m+n is 4 to 30.

Furthermore, the sea component of the sea-islands type composite fiber is preferably a cation dyeable polyester.

The false twist yarn includes a twist of two or more of the sea-islands type composite fiber, and can be suitably used in the fiber structure including the sea-islands type composite fiber and/or the false twist yarn in at least a part of the fiber structure.

The fiber does not undergo cracks of a sea component upon the volume expansion of a polymer having moisture absorbability that serves as an island component during a hot water treatment such as a dyeing treatment, thus rarely undergoes generation of dyeing specks and/or fluffs when the composite fiber is formed into a fiber structure such as a woven fabric or a knitted fabric, and has excellent quality. In addition, the sea-islands type composite fiber is reduced in elution of the polymer having moisture absorbability, thus has excellent moisture absorbability even after a hot water treatment such as a dyeing treatment, also has dry touch inherent to a polyester fiber when the sea component is polyester, and can be suitably used for, in particular, clothing applications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) to 1(m) show examples of the cross-sectional shape of the sea-islands type composite fiber.

FIGS. 2(a) to 2(c) show examples of the sea-island composite spinneret used in the method of manufacturing the sea-islands type composite fiber. FIG. 2(a) shows a front cross-sectional view of a main part constituting the sea-island composite spinneret, FIG. 2(b) shows a cross-sectional view of a part of a distribution plate, and FIG. 2(c) shows a cross-sectional view of a discharge plate.

FIG. 3 shows a part of an example of the distribution plate.

FIG. 4 shows an example of a distribution groove and distribution hole disposition in the distribution plate.

DESCRIPTION OF REFERENCE SIGNS

-   -   1: Sea component     -   2: Island component     -   3: Diameter of fiber     -   4: Circumscribed circle formed by connecting apexes of island         components disposed in outermost circle     -   5: Thickness of outermost layer     -   6: Diameter of island component     -   7: Measuring plate     -   8: Distribution plate     -   9: Discharge plate     -   10-(a): Measuring hole 1     -   10-(b): Measuring hole 2     -   11-(a): Distribution groove 1     -   11-(b): Distribution groove 2     -   12-(a): Distribution hole 1     -   12-(b): Distribution hole 2     -   13: Discharge loading hole     -   14: Reduction hole     -   15: Discharge hole     -   16: Annular groove

DETAILED DESCRIPTION

The sea-islands type composite fiber includes: an island component that is a polymer having moisture absorbability; a ratio (T/R) of a thickness T of an outermost layer to a diameter R of the fiber in a transverse cross section of the fiber of 0.05 to 0.25; and a moisture absorption rate difference (ΔMR) after a hot water treatment of 2.0 to 10.0%. The thickness of an outermost layer is a difference between a radius of the fiber and a radius of a circumscribed circle formed by connecting an apex of the island component disposed in an outermost circle, and represents a thickness of a sea component in the outermost layer.

A polymer having moisture absorbability (hereinafter may be simply referred to as a moisture absorbing polymer) generally tends to undergo volume expansion during a hot water treatment such as a dyeing treatment and easily elutes in hot water in nature. Therefore, when the moisture absorbing polymer is singly formed into a fiber, there is a problem that the moisture absorbing polymer is eluted by the hot water treatment, and the eluted portion causes dyeing specks and/or fluffs, resulting in the reduced quality. When the moisture absorbing polymer is a polymer copolymerized with a hydrophilic copolymerization component, there is also a problem that the hydrophilic copolymerization component is eluted by the hot water treatment, and the moisture absorbability is reduced after the hot water treatment.

Meanwhile, in the core-sheath type composite fiber in which the moisture absorbing polymer is disposed in the core, the moisture absorbing polymer disposed in the core undergoes volume expansion during a hot water treatment such as a dyeing treatment, and stress concentrates at the interface between the core component and the sheath component, resulting in cracks of the sheath component. Due to the cracks of the sheath component, dyeing specks and/or fluffs are generated, resulting in the reduced quality. Furthermore, there is another problem that the moisture absorbing polymer disposed in the core elutes from the cracked portion of the sheath component as a starting point, resulting in reduced moisture absorbability after the hot water treatment.

In the sea-islands type composite fiber in which the moisture absorbing polymer is disposed in the island, there is the same problem as in the core-sheath type composite fiber. The conventional sea-islands type composite fiber can be obtained by a conventionally known pipe sea-island composite spinneret disclosed in, for example, Japanese Patent Laid-open Publication No. 2007-100243, and has the technical limit of the thickness of the sea component in the outermost layer of about 150 nm. That is, since the thickness of the sea component in the outermost layer of the sea-islands type composite fiber is very thin as compared to the thickness of the sheath component of the core-sheath type composite fiber, cracks of the sea component easily occur due to the volume expansion of the moisture absorbing polymer disposed in the island caused by a hot water treatment such as a dyeing treatment. Due to the cracks of the sea component, dyeing specks and/or fluffs are generated, resulting in the reduced quality and, in addition, the moisture absorbing polymer disposed in the island elutes from the cracked portion of the sea component as a starting point, resulting in the reduced moisture absorbability after the hot water treatment.

We successfully obtained a sea-islands type composite fiber that resolves all the above problems, and exhibits high quality and high moisture absorbability even after a hot water treatment by dispersing the stress upon the volume expansion by the dispersed disposition of the moisture absorbing polymer, and setting the ratio (T/R) of a thickness T of an outermost layer to a diameter R of the fiber within a specific range.

The island component of the sea-islands type composite fiber is a polymer having moisture absorbability. The polymer having moisture absorbability is a polymer having a moisture absorption rate difference (ΔMR) of 2.0 to 30.0%. The moisture absorption rate difference (ΔMR) refers to the value measured by the method described in Examples. When ΔMR of the moisture absorbing polymer is 2.0% or more, a sea-islands type composite fiber having excellent moisture absorbability can be obtained in combination with the sea component. The ΔMR of the moisture absorbing polymer is more preferably 5.0% or more, further preferably 7.0% or more, particularly preferably 10.0% or more. When ΔMR of the moisture absorbing polymer is 30.0% or less, the process passability and handleability are good, and the durability in use after the polymer is formed into a sea-islands type composite fiber is also excellent. Therefore, it is preferable that ΔMR of the moisture absorbing polymer be 30.0% or less.

Specific examples of the island component of the sea-islands type composite fiber include, but are not limited to, moisture absorbing polymers such as a polyetherester, a polyether amide, a polyetherester amide, a polyamide, a thermoplastic cellulose derivative, and polyvinyl pyrrolidone. Among them, a polyetherester, a polyether amide, and a polyetherester amide containing a polyether as a copolymerization component are preferable because they have excellent moisture absorbability and, in particular, the polyetherester is preferable because it has excellent heat resistance, and provides good mechanical properties and color of the obtained sea-islands type composite fiber. Only one type of these moisture absorbing polymers may be used, or two or more types may be used in combination. A blend of these moisture absorbing polymers and a polyester, a polyamide, a polyolefin or the like may be used as a moisture absorbing polymer.

Specific examples of the polyether as the copolymerization component of the moisture absorbing polymer include, but are not limited to, homopolymers such as polyethylene glycol, polypropylene glycol, and polybutylene glycol, and copolymers such as a polyethylene glycol-polypropylene glycol copolymer and a polyethylene glycol-polybutylene glycol copolymer. Among these, polyethylene glycol, polypropylene glycol, and polybutylene glycol are preferable because they have good handleability in the production and use, and polyethylene glycol is particularly preferable because it has excellent moisture absorbability.

The polyether preferably has a number average molecular weight of 2,000 to 30,000 g/mol. When the polyether has a number average molecular weight of 2,000 g/mol or more, the moisture absorbability of the moisture absorbing polymer obtained by copolymerizing the polyether is high, and the sea-islands type composite fiber having excellent moisture absorbability is obtained when the moisture absorbing polymer is used as the island component. Therefore, it is preferable that the polyether have a number average molecular weight of 2,000 g/mol or more. The polyether more preferably has a number average molecular weight of 3,000 g/mol or more, further preferably 5,000 g/mol or more. When the polyether has a number average molecular weight of 30,000 g/mol or less, the polyether has high polycondensation reactivity, thus unreacted polyethylene glycol can be decreased, the elution of the moisture absorbing polymer of the island component into hot water during a hot water treatment such as a dyeing treatment is suppressed, and the moisture absorbability can be maintained even after the hot water treatment. Therefore, it is preferable that the polyether have a number average molecular weight of 30,000 g/mol or less. The polyether more preferably has a number average molecular weight of 25,000 g/mol or less, further preferably 20,000 g/mol or less.

The copolymerization ratio of the polyether is preferably 10 to 60% by weight. When the copolymerization ratio of the polyether is 10% by weight or more, the moisture absorbability of the moisture absorbing polymer obtained by copolymerizing the polyether is high, and the sea-islands type composite fiber having excellent moisture absorbability is obtained when the moisture absorbing polymer is used as the island component. Therefore, it is preferable that the copolymerization ratio of the polyether be 10% by weight or more. The copolymerization ratio of the polyether is more preferably 20% by weight or more, and further preferably 30% by weight or more. When the copolymerization ratio of the polyether is 60% by weight or less, unreacted polyethylene glycol can be decreased, the elution of the moisture absorbing polymer of the island component into hot water during a hot water treatment such as a dyeing treatment is suppressed, and the moisture absorbability can be maintained even after the hot water treatment. Therefore, it is preferable that the copolymerization ratio of the polyether be 60% by weight or less. The copolymerization ratio of the polyether is more preferably 55% by weight or less, and further preferably 50% by weight or less.

From the viewpoint of heat resistance and mechanical properties, it is preferable that the polyetherester contain an aromatic dicarboxylic acid and an aliphatic diol as main components, and a polyether as a copolymerization component, or contain an aromatic dicarboxylic acid and an aliphatic diol as main components, and a polyether and an alkylene oxide adduct of a bisphenol represented by General Formula (1) below as copolymerization components:

wherein m and n are integers of 2 to 20 and m+n is 4 to 30.

Specific examples of the aromatic dicarboxylic acid include, but are not limited to, terephthalic acid, isophthalic acid, phthalic acid, 5-sodium sulfoisophthalic acid, 5-lithium sulfoisophthalic acid, 5-(tetraalkyl) phosphonium sulfoisophthalic acid, 4,4′-diphenyl dicarboxylic acid, and 2,6-naphthalene dicarboxylic acid.

Specific examples of the aliphatic diol include, but are not limited to, ethylene glycol, 1,3-propanediol, 1,4-butanediol, hexanediol, cyclohexanediol, diethylene glycol, hexamethylene glycol, and neopentyl glycol. Among these, ethylene glycol, propylene glycol, and 1,4-butanediol are preferable because of good handleability in the production and use, ethylene glycol can be suitably employed from the viewpoint of the heat resistance and mechanical properties, and 1,4-butanediol can be suitably employed from the viewpoint of crystallinity.

When the polyetherester contains the polyether and the alkylene oxide adduct of a bisphenol represented by General Formula (1) as copolymerization components, the polyetherester has good forming processability, the mechanical properties of the obtained sea-islands type composite fiber is high, generation of unevenness of fineness can be suppressed, and dyeing specks and/or fluffs are small, resulting in the good quality. Therefore, it is preferable that the polyetherester contain the polyether and the alkylene oxide adduct of a bisphenol represented by General Formula (1) as copolymerization components.

In the alkylene oxide adduct of a bisphenol represented by General Formula (1), m+n is preferably 4 to 30. When m+n is 4 or more, the polyetherester has good forming processability, generation of unevenness of fineness in the obtained sea-islands type composite fiber can be suppressed, and dyeing specks and/or fluffs are small, resulting in the good quality. Therefore, it is preferable that m+n be 4 or more. When m+n is 30 or less, the polyetherester has good heat resistance and color, and the mechanical properties and color of the obtained sea-islands type composite fiber are good. Therefore, it is preferable that m+n be 30 or less. More preferably, m+n is 20 or less, and further preferably, 10 or less.

Specific examples of the alkylene oxide adduct of a bisphenol represented by General Formula (1) include, but are not limited to, an ethylene oxide adduct of bisphenol A and an ethylene oxide adduct of bisphenol S. Among these, the ethylene oxide adduct of bisphenol A is preferable because of the good handleability in the production and use, and also can be suitably employed from the viewpoint of the heat resistance and mechanical properties.

When the polyetherester includes the polyether and the alkylene oxide adduct of a bisphenol represented by General Formula (1) as copolymerization components, it is preferable that the copolymerization ratio of the polyether be 10 to 45% by weight, and the copolymerization ratio of the alkylene oxide adduct of a bisphenol be 10 to 30% by weight. When the copolymerization ratio of the polyether is 10% by weight or more, the moisture absorbability of the moisture absorbing polymer obtained by copolymerizing the polyether is high, and the sea-islands type composite fiber having excellent moisture absorbability is obtained when the moisture absorbing polymer is used as the island component. Therefore, it is preferable that the copolymerization ratio of the polyether be 10% by weight or more. The copolymerization ratio of the polyether is more preferably 20% by weight or more, and further preferably 30% by weight or more. When the copolymerization ratio of the polyether is 45% by weight or less, unreacted polyethylene glycol can be decreased, the elution of the moisture absorbing polymer of the island component into hot water during a hot water treatment such as a dyeing treatment is suppressed, and the moisture absorbability can be maintained even after the hot water treatment. Therefore, it is preferable that the copolymerization ratio of the polyether be 45% by weight or less. The copolymerization ratio of the polyether is more preferably 40% by weight or less, and further preferably 35% by weight or less. When the copolymerization ratio of the alkylene oxide adduct of a bisphenol is 10% by weight or more, the polyetherester has good forming processability, generation of unevenness of fineness in the obtained sea-islands type composite fiber can be suppressed, and dyeing specks and/or fluffs are small, resulting in the good quality. Therefore, it is preferable that the copolymerization ratio of the alkylene oxide adduct of a bisphenol be 10% by weight or more. The copolymerization ratio of the alkylene oxide adduct of a bisphenol is more preferably 12% by weight or more, and further preferably 14% by weight or more. When the copolymerization ratio of the alkylene oxide adduct of a bisphenol is 30% by weight or less, the polyetherester has good heat resistance and color, and the mechanical properties and color of the obtained sea-islands type composite fiber are good. Therefore, it is preferable that the copolymerization ratio of the alkylene oxide adduct of a bisphenol be 30% by weight or less. The copolymerization ratio of the alkylene oxide adduct of a bisphenol is more preferably 25% by weight or less, and further preferably 20% by weight or less.

The island component of the sea-islands type composite fiber is preferably a polymer having crystallinity. When the island component has crystallinity, a melting peak associated with the melting of the crystal is observed in the measurement of the extrapolated melting onset temperature by the method described in the Examples. When the island component has crystallinity, elution of the moisture absorbing polymer of the island component into hot water during a hot water treatment such as a dyeing treatment is suppressed, and thus moisture absorbability can be maintained even after the hot water treatment. Therefore, it is preferable that the island component have crystallinity.

The sea component of the sea-islands type composite fiber preferably has crystallinity. When the sea component has crystallinity, a melting peak associated with the melting of the crystal is observed in the measurement of the extrapolated melting onset temperature by the method described in the Examples. When the sea component has crystallinity, fusion between fibers due to the contact with a heating roller and a heating heater in the drawing and false twisting processes is suppressed, thus the deposit, yarn breakage and fluffs generation on the heating roller, the heating heater, and the guide are small, the process passability is good and, in addition, generation of dyeing specks and/or fluffs are small when the fiber is formed into a fiber structure such as a woven fabric and a knitted fabric, resulting in excellent quality. Elution of the sea component into hot water during a hot water treatment such as a dyeing treatment is also suppressed. Therefore, it is preferable that the sea component have crystallinity.

Specific examples of the sea component of the sea-islands type composite fiber include, but are not limited to, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyamides such as nylon 6 and nylon 66, and polyolefins such as polyethylene and polypropylene. Among these, polyesters are preferable because they are excellent in mechanical properties and durability. When the sea component is a hydrophobic polymer such as a polyester or a polyolefin, both the moisture absorbability provided by the moisture absorbing polymer of the island component and the dry touch provided by the hydrophobic polymer of the sea component can be obtained and a fiber structure having excellent wearing comfort can be obtained. Therefore, it is preferable that the sea component be a hydrophobic polymer such as a polyester or a polyolefin.

Specific examples of the polyester according to the sea component of the sea-islands type composite fiber include, but are not limited to, aromatic polyesters such as polyethylene terephthalate, polypropylene terephthalate, and polybutylene terephthalate, and aliphatic polyesters such as polylactic acid and polyglycolic acid. Among these, polyethylene terephthalate, polypropylene terephthalate, and polybutylene terephthalate are preferable because they are excellent in mechanical properties and durability, and have good handleability in the production and use. The polyethylene terephthalate is preferable because it gives a tension and elasticity feeling peculiar to polyester fiber, and polybutylene terephthalate is preferable because it has high crystallinity.

The sea component of the sea-islands type composite fiber is preferably a cation dyeable polyester. When a polyester has an anionic site such as a sulfonic acid group, it has cationic dyeability due to the interaction with a cationic dye having a cation site. When the sea component is a cation dyeable polyester, vivid coloring is exhibited and dye contamination can be prevented in combined use with a polyurethane fiber. Therefore, it is preferable that the sea component be a cation dyeable polyester. Specific examples of the copolymerization component of the cation dyeable polyester include a metal salt of 5-sulfoisophthalic acid, and examples of the metal salt include, but are not limited to, a lithium salt, a sodium salt, a potassium salt, a rubidium salt, and a cesium salt. Among these, the lithium salt and the sodium salt are preferable and, in particular, the sodium salt can be suitably employed because it is excellent in crystallinity.

The sea-islands type composite fiber may be one in which various modifications are made by adding secondary additives to the sea component and/or the island component. Specific examples of the secondary additives include, but are not limited to, a compatibilizer, a plasticizer, an antioxidant, an ultraviolet absorber, an infrared absorber, a fluorescent whitening agent, a release agent, an antibacterial agent, a nucleating agent, a thermal stabilizer, an antistatic agent, a coloring inhibitor, a regulator, a delustering agent, a defoaming agent, a preservative, a gelling agent, a latex, a filler, an ink, a colorant, a dye, a pigment, and a perfume. These secondary additives may be used singly or in combination.

The extrapolated melting onset temperature of the sea-islands type composite fiber is preferably 150 to 300° C. The extrapolated melting onset temperature of the sea-islands type composite fiber refers to the value calculated by the method described in the Examples. When a plurality of melting peaks were observed, the extrapolated melting onset temperature was calculated from the melting peak at the lowest temperature. When the extrapolated melting onset temperature of the sea-islands type composite fiber is 150° C. or more, fusion between fibers due to the contact with a heating roller and a heating heater in the drawing and false twisting processes is suppressed, thus the deposit, yarn breakage and fluffs generation on the heating roller, the heating heater, and the guide are small, the process passability is good and, in addition, generation of dyeing specks and/or fluffs are small when the fiber is formed into a fiber structure such as a woven fabric and a knitted fabric, resulting in excellent quality. Therefore, it is preferable that the extrapolated melting onset temperature of the sea-islands type composite fiber be 150° C. or more. The extrapolated melting onset temperature of the sea-islands type composite fiber is more preferably 170° C. or more, further preferably 190° C. or more, particularly preferably 200° C. or more. When the extrapolated melting onset temperature of the sea-islands type composite fiber is 300° C. or less, the yellowing due to thermal deterioration is suppressed in the melt spinning process, and a sea-islands type composite fiber having good color is obtained. Therefore, it is preferable that the extrapolated melting onset temperature of the sea-islands type composite fiber be 300° C. or less.

The sea-islands type composite fiber includes a ratio (T/R) of a thickness T of an outermost layer to a diameter R of the fiber in a transverse cross section of the fiber of 0.05 to 0.25. The thickness of an outermost layer is a difference between a radius of the fiber and a radius of a circumscribed circle formed by connecting an apex of the island component disposed in an outermost circle, and represents a thickness of a sea component in the outermost layer. The ratio (T/R) of a thickness T of an outermost layer to a diameter R of the fiber refers to the value calculated by the method described in the Examples. When the sea-islands type composite fiber includes T/R of 0.05 or more, the thickness of the outermost layer relative to the fiber diameter is sufficient, thus the cracks of the sea component upon the volume expansion of the moisture absorbing polymer disposed in the island due to a hot water treatment such as a dyeing treatment can be suppressed, generation of dyeing specks and/or fluffs caused by the cracks of the sea component is small, the fiber has excellent quality, elution of the moisture absorbing polymer is also suppressed, and thus high moisture absorbability is exhibited even after the hot water treatment. Also, by dyeing the sea component, sufficient coloring can be obtained, and a fiber and a fiber structure having high quality from the viewpoint of coloring can be obtained. The sea-islands type composite fiber more preferably includes T/R of 0.07 or more, further preferably 0.09 or more, particularly preferably 0.10 or more. When the sea-islands type composite fiber includes T/R of 0.25 or less, the volume expansion of the moisture absorbing polymer disposed in the island is not impaired by the thickness of the outermost layer with respect to the fiber diameter, moisture absorbability provided by the moisture absorbing polymer is exhibited, and thus a fiber and a fiber structure having high moisture absorbability can be obtained. The sea-islands type composite fiber more preferably includes T/R of 0.22 or less, further preferably 0.20 or less.

The thickness T of an outermost layer of the sea-islands type composite fiber is preferably 500 to 3,000 nm. The thickness T of an outermost layer refers to the value calculated by the method described in the Examples. When the thickness T of an outermost layer of the sea-islands type composite fiber is 500 nm or more, the thickness of the outermost layer is sufficient, thus the cracks of the sea component upon the volume expansion of the moisture absorbing polymer disposed in the island due to a hot water treatment such as a dyeing treatment can be suppressed, generation of dyeing specks and/or fluffs caused by the cracks of the sea component is small, the fiber has excellent quality, elution of the moisture absorbing polymer is also suppressed, and thus high moisture absorbability is exhibited even after the hot water treatment. Also, by dyeing the sea component, sufficient coloring can be obtained, and a fiber and a fiber structure having high quality from the viewpoint of coloring can be obtained. Therefore, it is preferable that the thickness T of an outermost layer of the sea-islands type composite fiber be 500 nm or more. The thickness T of an outermost layer of the sea-islands type composite fiber is more preferably 700 nm or more, further preferably 800 nm or more, particularly preferably 1,000 nm or more. When the thickness T of an outermost layer of the sea-islands type composite fiber is 3,000 nm or less, the volume expansion of the moisture absorbing polymer disposed in the island is not impaired by the thickness of the outermost layer with respect to the fiber diameter, moisture absorbability provided by the moisture absorbing polymer is exhibited, and thus a fiber and a fiber structure having high moisture absorbability can be obtained. Therefore, it is preferable that the thickness T of an outermost layer of the sea-islands type composite fiber be 3,000 nm or less. The thickness T of an outermost layer of the sea-islands type composite fiber is more preferably 2,500 nm or less, further preferably 2,000 nm or less.

The number of the island of the sea-islands type composite fiber is preferably 3 to 10,000. When the number of the islands of the sea-islands type composite fiber is 3 or more, the dispersed disposition of the moisture absorbing polymer, the island component, disperses the stress generated by the volume expansion of the moisture absorbing polymer during a hot water treatment such as a dyeing treatment, and thus the cracks of the sheath component due to the stress concentration, which is a problem of the conventional core-sheath type composite fiber, can be suppressed. Therefore, it is preferable that the number of the islands of the sea-islands type composite fiber be 3 or more. The number of the islands of the sea-islands type composite fiber is more preferably 6 or more, further preferably 12 or more, particularly preferably 20 or more. When the number of the islands of the sea-islands type composite fiber is 10,000 or less, the disposition of the island component in transverse cross section of the fiber can be precisely controlled, and a fiber and a fiber structure having high quality from the viewpoint of feel and coloring can be obtained. Therefore, it is preferable that the number of the islands of the sea-islands type composite fiber be 10,000 or less. The number of the islands of the sea-islands type composite fiber is more preferably 5,000 or less, further preferably 1,000 or less.

In the sea-islands type composite fiber, the diameter r of the island component in the transverse cross section of the fiber is preferably 10 to 5,000 nm. The diameter r of the island component refers to the value calculated by the method described in the Examples. When the diameter r of the island component in the transverse cross section of the fiber is 10 nm or more, the moisture absorbability provided by the moisture absorbing polymer of the island component dispersively disposed in the transverse cross section of the fiber is exhibited. Therefore, it is preferable that the diameter r of the island component in the transverse cross section of the fiber be 10 nm or more. The diameter r of the island component in the transverse cross section of the fiber of the sea-islands type composite fiber is more preferably 100 nm or more, further preferably 500 nm or more. When the diameter r of the island component in the transverse cross section of the fiber is 5,000 nm or less, the stress generated by the volume expansion of the moisture absorbing polymer disposed in the island component during a hot water treatment such as a dyeing treatment can be decreased, and the cracks of the sea component can be suppressed. Therefore, it is preferable that the diameter r of the island component in the transverse cross section of the fiber be 5,000 nm or less. The diameter r of the island component in the transverse cross section of the fiber of the sea-islands type composite fiber is more preferably 3,000 nm or less, further preferably 2,000 nm or less.

In the sea-islands type composite fiber, the island component is preferably disposed to from 2 to 100 circles in the transverse cross section of the fiber. The island components disposed concentrically in the transverse cross section of the fiber is defined as one circle, and the number of the concentric circles having different diameters is the number of the circles. When one island component is disposed at the center of the transverse cross section of the fiber, the one island component disposed at the center is defined as one circle. FIGS. 1(a) to 1(m) are examples of the cross-sectional shape of the sea-islands type composite fiber. The island component is disposed to form one circle in FIGS. 1(b) and (c), two circles in FIGS. 1(a), (d), (h), (i), (j), (k), and (m), three circles in FIGS. 1(e), (g), and (l), and seven circles in FIG. 1(f). For the stress generated by the volume expansion of the moisture absorbing polymer during a hot water treatment such as a dyeing treatment, those skilled in the art analyzed in detail the stress distribution in the transverse cross section of the fiber, and obtained a result that, in the core-sheath type composite fiber, the stress is maximum at the interface between the core component and the sheath component, and in the sea-islands type composite fiber in which the island component is disposed to form one circle as shown in FIGS. 1(b) and (c), the stress is maximum at the interface between the fiber surface side of the island component and the sea component. That is, we found that in the core-sheath type composite fiber, breaks are generated at the interface between the core component and the sheath component which is subjected to the maximum stress upon the volume expansion of the moisture absorbing polymer of the core component, and these breaks propagate to the fiber surface, whereby the cracks of the sheath component are generated. Similarly, in the sea-islands type composite fiber in which the island component is disposed to form one circle, breaks are generated at the interface between the fiber surface side of the island component and the sea component which is subjected to the maximum stress upon the volume expansion of the moisture absorbing polymer of the island component, and these breaks propagate to the fiber surface, whereby the cracks of the sea component are generated. In contrast, in the sea-islands type composite fiber in which the island component is disposed to form two or more circles in the transverse cross section of the fiber, the stress is maximum between the fiber internal side of the island component disposed in the outermost circle and the fiber surface side of the island component disposed one circle inward from the outermost circle, and propagation of breaks to the fiber surface is blocked, thereby cracking of the sea component is suppressed. Thus, such a disposition is preferable. In the transverse cross section of the fiber of the sea-islands type composite fiber, the island component is more preferably disposed to form three or more circles, and is further preferably disposed to form four or more circles. When the island component is disposed to form 100 or less circles, a space can be provided between neighboring island components, thus the moisture absorbing polymer of the island component can undergo the volume expansion due to the moisture absorption, and a sea-islands type composite fiber having excellent moisture absorbability can be obtained. Therefore, such a disposition is preferable.

The sea-islands type composite fiber preferably includes a ratio (r1/r2) of a diameter r1 of the island component disposed to pass through a center of the transverse cross section of the fiber to a diameter r2 of other island components of 1.1 to 10.0. The ratio (r1/r2) of a diameter r1 of the island component disposed to pass through a center of the transverse cross section of the fiber to a diameter r2 of other island components refers to the value calculated by the method described in the Examples. When the diameter r2 of other island components is smaller than the diameter r1 of the island component disposed to pass through a center of the transverse cross section of the fiber, r1/r2 is more than 1.0. Examples of the cross-sectional shape of the sea-islands type composite fiber having such r1/r2 include FIGS. 1(k) to (m). When the sea-islands type composite fiber includes r1/r2 of 1.1 or more, the diameter r2 of other island components is smaller than the diameter r1 of the island component disposed to pass through a center of the transverse cross section of the fiber, thus the stress generated by the volume expansion of the moisture absorbing polymer of the island component close to the fiber surface can be decreased, and the cracks of the sea component can be suppressed. Therefore, it is preferable that the sea-islands type composite fiber include r1/r2 of 1.1 or more. The sea-islands type composite fiber more preferably includes r1/r2 of 1.2 or more, further preferably includes r1/r2 of 1.5 or more. When the sea-islands type composite fiber includes r1/r2 of 10.0 or less, stress generated by the volume expansion of the moisture absorbing polymer of the island component disposed to pass through a center of the transverse cross section of the fiber can be absorbed by other island components. Thus, the propagation of breaks to the fiber surface is blocked, and the cracks of the sea component can be suppressed. Therefore, it is preferable that the sea-islands type composite fiber include r1/r2 of 10.0 or less. The sea-islands type composite fiber more preferably includes r1/r2 of 7.0 or less, further preferably 5.0 or less.

The shape of the island component in the transverse cross section of the fiber in the sea-islands type composite fiber is not particularly limited, and may be a circular cross section of a perfect circle or non-circular cross section. Specific examples of the non-circular cross section include, but are not limited to, a multifoil, a polygon, a flat shape, and an oval. Among these, when the island component has a circular cross section of a perfect circle, the stress is evenly generated over the circumference and not concentrated when the moisture absorbing polymer disposed in the island undergoes volume expansion, and thus the cracks of the sea component can be suppressed. Therefore, it is preferable that the island component have a circular cross section. The shape of the center side of the island component disposed in the outermost circle in the transverse cross section of the fiber is preferably non-circular. In this example, in the island component disposed in the outermost circle, the stress is concentrated not on the surface side of the fiber but on the non-circular portion on the center side of the fiber, thus the cracks of the sea component to the fiber surface can be suppressed. Therefore, it is preferable that the shape of the center side of the island component disposed in the outermost circle in the transverse cross section of the fiber be non-circular.

The sea-islands type composite fiber preferably includes a composite ratio (a weight ratio) of the sea component/island component of 50/50 to 90/10. The composite ratio (the weight ratio) of the sea component/island component of the sea-islands type composite fiber refers to the value calculated by the method described in the Examples. When the sea-islands type composite fiber includes a composite ratio of the sea component of 50% by weight or more, the sea component gives a tension feeling, elasticity feeling, and a dry touch. In addition, the cracks of the sea component due to an external force during drawing and false twisting and the cracks of a sea component upon the volume expansion of the moisture absorbing polymer of the island component during moisture absorption and water absorption are suppressed, thus the reduction of quality due to the generation of dyeing specks and/or fluffs and the reduction of moisture absorbability due to the elution of the polymer having moisture absorbability of the island component into hot water during a hot water treatment such as a dyeing treatment are suppressed. Therefore, it is preferable that the sea-islands type composite fiber include a composite ratio of the sea component of 50% by weight or more. The sea-islands type composite fiber more preferably includes a composite ratio of the sea component of 55% by weight or more, further preferably 60% by weight or more. When the sea-islands type composite fiber includes a composite ratio of the sea component of 90% by weight or less, that is, the sea-islands type composite fiber includes a composite ratio of the island component of 10% by weight or more, moisture absorbability of the moisture absorbing polymer of the island component is exhibited, and the sea-islands type composite fiber having excellent moisture absorbability can be obtained. Therefore, it is preferable that the sea-islands type composite fiber include a composite ratio of the sea component of 90% by weight or less, that is, the sea-islands type composite fiber include a composite ratio of the island component of 10% by weight or more. The sea-islands type composite fiber more preferably includes a composite ratio of the sea component of 85% by weight or less, further preferably 80% by weight or less.

The fineness of the sea-islands type composite fiber as a multifilament is not particularly limited, and may be appropriately selected depending on the application and required properties. It is preferably 10 to 500 dtex. The fineness refers to the value measured by the method described in the Examples. When the sea-islands type composite fiber has a fineness of 10 dtex or more, the yarn breakage is small, the process passability is good, in addition, the generation of fluffs is small in use, and the durability is excellent. Therefore, it is preferable that the sea-islands type composite fiber have a fineness of 10 dtex or more. The sea-islands type composite fiber more preferably has a fineness of 30 dtex or more, further preferably 50 dtex or more. When the sea-islands type composite fiber has a fineness of 500 dtex or less, the flexibility of the fiber and fiber structure is not impaired. Therefore, it is preferable that the sea-islands type composite fiber have a fineness of 500 dtex or less. The sea-islands type composite fiber more preferably has a fineness of 400 dtex or less, further preferably 300 dtex or less.

The single yarn fineness of the sea-islands type composite fiber is not particularly limited, and may be appropriately selected depending on the application and required properties. It is preferably 0.5 to 4.0 dtex. The single yarn fineness refers to the value obtained by dividing the fineness measured by the method described in the Examples by the number of the single yarn. When the sea-islands type composite fiber has a single yarn fineness of 0.5 dtex or more, the yarn breakage is small, the process passability is good, in addition, the generation of fluffs is small in use, and the durability is excellent. Therefore, it is preferable that the sea-islands type composite fiber have a single yarn fineness of 0.5 dtex or more. The sea-islands type composite fiber more preferably has a single yarn fineness of 0.6 dtex or more, further preferably 0.8 dtex or more. When the sea-islands type composite fiber has a single yarn fineness of 4.0 dtex or less, the flexibility of the fiber and fiber structure is not impaired. Therefore, it is preferable that the sea-islands type composite fiber have a single yarn fineness of 4.0 dtex or less. The sea-islands type composite fiber more preferably has a single yarn fineness of 2.0 dtex or less, further preferably 1.5 dtex or less.

The strength of the sea-islands type composite fiber is not particularly limited, and may be appropriately selected depending on the application and required properties. It is preferably 2.0 to 5.0 cN/dtex from the viewpoint of the mechanical properties. Strength refers to the value measured by the method described in the Examples. When the sea-islands type composite fiber has a strength of 2.0 cN/dtex or more, generation of fluffs is small in use, and the durability is excellent. Therefore, it is preferable that the sea-islands type composite fiber have a strength of 2.0 cN/dtex or more. The sea-islands type composite fiber more preferably has a strength of 2.5 cN/dtex or more, further preferably 3.0 cN/dtex or more. When the sea-islands type composite fiber has a strength of 5.0 cN/dtex or less, the flexibility of the fiber and fiber structure is not impaired. Therefore, it is preferable that the sea-islands type composite fiber have a strength of 5.0 cN/dtex or less.

The elongation percentage of the sea-islands type composite fiber is not particularly limited, and may be appropriately selected depending on the application and required properties. It is preferably 10 to 60% from the viewpoint of durability. Elongation percentage refers to the value measured by the method described in the Examples. When the sea-islands type composite fiber has an elongation percentage of 10% or more, the abrasion resistance of the fiber and the fiber structure is good, thus the generation of fluffs is small in use, and the durability is good. Therefore, it is preferable that the sea-islands type composite fiber have an elongation percentage of 10% or more. The sea-islands type composite fiber more preferably has an elongation percentage of 15% or more, further preferably 20% or more. When the sea-islands type composite fiber has an elongation percentage of 60% or less, the dimensional stability of the fiber and the fiber structure is good. Therefore, it is preferable that the sea-islands type composite fiber have an elongation percentage of 60% or less. The sea-islands type composite fiber more preferably has an elongation percentage of 55% or less, further preferably 50% or less.

The sea-islands type composite fiber has a moisture absorption rate difference (ΔMR) after a hot water treatment of 2.0 to 10.0%. The moisture absorption rate difference (ΔMR) after a hot water treatment refers to the value measured by the method described in the Examples. ΔMR is the difference between the moisture absorption rate at a temperature of 30° C. and a humidity of 90% RH, which are an assumed temperature and humidity inside clothes after light exercise, and the moisture absorption rate at a temperature of 20° C. and a humidity of 65% RH, which are an ambient temperature and humidity. That is, ΔMR is an index of the moisture absorbability. The higher the value of ΔMR is, the more the wearing comfort improves. The moisture absorption rate difference (ΔMR) is a value after a hot water treatment, and is very important value in that it shows that the moisture absorbability is exhibited even after a hot water treatment such as a dyeing treatment. When ΔMR after a hot water treatment of the sea-islands type composite fiber is 2.0% or more, a stuffy feeling in clothes is small, and wearing comfort is exhibited. The sea-islands type composite fiber more preferably includes ΔMR after a hot water treatment of 2.5% or more, further preferably 3.0% or more, particularly preferably 4.0% or more. When the sea-islands type composite fiber includes ΔMR after a hot water treatment of 10.0% or less, the process passability and handleability are good, and the durability in use is also excellent.

The cross-sectional shape of the sea-islands type composite fiber is not particularly limited, may be appropriately selected depending on the application and required properties, and may be a circular cross section of a perfect circle or non-circular cross section. Specific examples of the non-circular cross section include, but are not limited to, a multifoil, a polygon, a flat shape, and an oval.

The form of the sea-islands type composite fiber is not particularly limited, and may be in any form such as a monofilament, a multifilament, and a staple.

The sea-islands type composite fiber can be processed into a false twist yarn or a twist yarn in the same way as in usual fibers, and can be weaved or knitted in the same way as in usual fibers.

The form of the fiber structure including the sea-islands type composite fiber and/or the false twist yarn is not particularly limited, and the sea-islands type composite fiber and/or the false twist yarn can be formed into a woven fabric, a knitted fabric, a pile fabric, a nonwoven fabric, a spun yarn, a wad or the like according to a known method. The fiber structure including the sea-islands type composite fiber and/or the false twist yarn may be any woven or knitted structure. A plain weave, a twill weave, a satin weave, or a weave changed from these weaves; or warp knitting, weft knitting, circular knitting, lace stitching, knitting or stitching changed from these knitting or stitching or the like can be suitably employed.

The sea-islands type composite fiber may be combined with other fibers by union weaving or union knitting during the formation of the fiber structure, or may be combined with other fibers to form a combined filament yarn and then the combined filament yarn may be formed into the fiber structure.

Next, a method of manufacturing the sea-islands type composite fiber will be described below.

As the method of manufacturing the sea-islands type composite fiber, a known melt spinning method, a drawing method, a crimping process method such as a false twisting method can be employed.

The sea component and the island component are preferably dried before the melt spinning to reduce the water content to 300 ppm or less. When the water content is 300 ppm or less, molecular weight reduction due to hydrolysis and foaming due to moisture during the melt spinning is suppressed, and thus spinning can be stably performed. Therefore, it is preferable that the water content be 300 ppm or less. The water content is more preferably 100 ppm or less, further preferably 50 ppm or less.

A preliminarily dried chip is supplied to a melt spinning machine such as an extruder type machine and a pressure melter type machine, and the sea component and the island component are separately melted and measured by a measuring pump. Thereafter, the measured sea component and island component are loaded into heated spinning packs at a spinning block, the melted polymers are filtered within the spinning packs, and then joined by a sea-island composite spinneret below and discharged as a sea-island structure from the spinneret to form a fiber yarn.

As the sea-island composite spinneret, for example, the conventionally known pipe sea-island composite spinneret in which pipes are disposed and which is disclosed in Japanese Patent Laid-open Publication No. 2007-100243 can be used for manufacturing. However, the conventional pipe sea-island composite spinneret has a technical limit on the thickness of the sea component of the outermost layer around 150 nm, and has a difficulty to satisfy the ratio (T/R) of a thickness T of an outermost layer to a diameter R of the fiber in the transverse cross section of our fiber. Therefore, the method described in Japanese Patent Laid-open Publication No. 2011-174215 in which a sea-island composite spinneret is used is preferably used.

As an example of the sea-island composite spinneret, the sea-island composite spinneret composed of the members shown in FIGS. 2(a) to 4 will be described. FIGS. 2(a) to (c) are illustrations to schematically describe an example of the sea-island composite spinneret used in our methods. FIG. 2(a) shows a front cross-sectional view of a main part that constitutes a sea-island composite spinneret, FIG. 2(b) shows a cross-sectional view of a part of a distribution plate, and FIG. 2(c) shows a cross-sectional view of a part of a discharge plate. FIGS. 2(b) and 2(c) show a distribution plate and a discharge plate that constitute FIG. 2(a). FIG. 3 shows a plan view of the distribution plate, and FIG. 4 shows an enlarged view of a part of the distribution plate in which each groove and hole are related to one discharge hole.

Hereinafter, the process from formation of the composite polymer flow through the measuring plate and the distribution plate to the discharge from the discharge hole of the discharge plate will be described. From the upstream of the spinning pack, a polymer A (an island component) and a polymer B (a sea component) are poured into a measuring hole for the polymer A (10-(a)) and a measuring hole for the polymer B (10-(b)) on the measuring plate in FIGS. 2(a) to 2(c), measured by a hole restriction drilled at the lower end, and then poured into the distribution plate. In the distribution plate, distribution grooves 11 (FIG. 3: 11-(a) and 11-(b)) to join the polymers flowing in from the measuring holes 10 and distribution holes 12 (FIG. 4: 12-(a) and 12-(b)) to flow the polymers downstream on the lower surface of the distribution groove are drilled. To form a layer composed of the polymer B, the sea component, in the outermost layer of the composite polymer flow, an annular groove 16 having distribution holes drilled on the bottom as shown in FIG. 3 is placed.

The composite polymer flow composed of the polymer A and the polymer B discharged from the distribution plate flows into a discharge plate 9 from a discharge loading hole 13. Then, the composite polymer flow is reduced in the cross-sectional direction along the polymer flow by a reduction hole 14 during loading of the flow into the discharge hole having a desired diameter, and discharged from a discharge hole 15 with the cross-sectional form formed in the distribution plate being maintained.

The fiber yarn discharged from the sea-island composite spinneret is cooled and solidified by a cooling device, taken up by a first godet roller, and wound by a winder through a second godet roller as a wound yarn. To improve the spinning operability, productivity, and mechanical properties of the fiber, a heating cylinder or a heat insulating cylinder having a length of 2 to 20 cm may be placed under the spinneret as necessary. An oil may be fed to the fiber yarn using an oiling device, and entanglement may be imparted to the fiber yarn using the entangling device.

The spinning temperature in the melt spinning may be appropriately selected depending on the melting points and the heat resistance of the sea component and the island component, but it is preferably 240 to 320° C. When the spinning temperature is 240° C. or more, the elongation viscosity of the fiber yarn discharged from the spinneret is sufficiently reduced, thus the discharge is stabilized, further, spinning tension does not excessively increase, and yarn breakage is suppressed. Therefore, it is preferable that the spinning temperature be 240° C. or more. The spinning temperature is more preferably 250° C. or more, further preferably 260° C. or more. When the spinning temperature is 320° C. or less, thermal decomposition during spinning can be suppressed, and deterioration of mechanical properties of the fiber and coloring can be suppressed. Therefore, it is preferable that the spinning temperature be 320° C. or less. The spinning temperature is more preferably 310° C. or less, further preferably 300° C. or less.

The spinning speed in the melt spinning may be appropriately selected depending on the compositions of the sea component and the island component, the spinning temperature and the like. In the two-step process in which drawing or false twisting is performed separately after melt spinning is performed and the yarn is wound, the spinning speed is preferably 500 to 6,000 m/min. When the spinning speed is 500 m/min or more, the traveling yarn is stabilized, and yarn breakage can be suppressed. Therefore, it is preferable that the spinning speed be 500 m/min or more. In the two-step process, the spinning speed is more preferably 1,000 m/min or more, further preferably 1,500 m/min or more. When the spinning speed is 6,000 m/min or less, due to suppression of spinning tension, stable spinning can be carried out without yarn breakage. Therefore, it is preferable that the spinning speed be 6,000 m/min or less. In the two-step process, the spinning speed is more preferably 4,500 m/min or less, further preferably 4,000 m/min or less. In the one-step process in which spinning and drawing are simultaneously performed without winding up once, it is preferable that the spinning speed of the low speed roller be set to 500 to 5,000 m/min and the spinning speed of the high speed roller be set to 2,500 to 6,000 m/min. When the spinning speeds of the low speed roller and the high speed roller are within the above-mentioned ranges, the traveling yarn is stabilized, yarn breakage can be suppressed, and stable spinning can be performed. Therefore, it is preferable that the spinning speeds of the low speed roller and the high speed roller be within the above-mentioned ranges. In the one-step process, it is more preferable that the spinning speed of the low speed roller be set to 1,000 to 4,500 m/min, and the spinning speed of the high speed roller be set to 3,500 to 5,500 m/min, and it is further preferable that the spinning speed of the low speed roller be set to 1,500 to 4,000 m/min, and the spinning speed of the high speed roller be set to 4,000 to 5,000 m/min.

When drawing is performed in the one-step process or the two-step process, the one-step drawing method or the multi-step drawing method having two or more steps may be used. The heating method in drawing is not particularly limited as long as the device can directly or indirectly heat the traveling yarn. Specific examples of the heating method include, but are not limited to, a heating roller method, a thermal pin method, a hot plate method, liquid baths such as a warm water bath and a hot water bath, gas baths such as a hot air bath and a steam bath, and a laser method. These heating methods may be used singly, or in combination. As the heating method, from the viewpoint of the control of the heating temperature, the uniform heating of the traveling yarn, and the simple device, contact with a heating roller, contact with a thermal pin, contact with a hot plate, and dipping in a liquid bath can be suitably employed.

When drawing is performed, the drawing temperature may be appropriately selected depending on the extrapolated melting onset temperature of the polymers of the sea component and the island component, and the strength and elongation percentage of the fiber after drawing and the like, but it is preferably 50 to 150° C. When the drawing temperature is 50° C. or more, the preheating of the yarn supplied for drawing is sufficiently performed, thermal deformation during drawing is uniform, generation of unevenness of fineness can be suppressed, dyeing specks and/or fluffs are small, and thus the quality is good. Therefore, it is preferable that the drawing temperature be 50° C. or more. The drawing temperature is more preferably 60° C. or more, and further preferably 70° C. or more. When the drawing temperature is 150° C. or less, fusion between fibers and thermal decomposition due to the contact with the heating roller can be suppressed, and the process passability and quality are good. In addition, the slipperiness of the fiber to the drawing roller is good, thus yarn breakage is suppressed, and stable drawing can be performed. Therefore, it is preferable that the drawing temperature be 150° C. or less. The drawing temperature is more preferably 145° C. or less, and further preferably 140° C. or less. The heat setting at 60 to 150° C. may be performed as needed.

When drawing is performed, the drawing rate may be appropriately selected depending on the elongation percentage of the fiber before drawing, the strength and the elongation percentage of the fiber after drawing and the like, but it is preferably 1.02 to 7.0 times. When the drawing rate is 1.02 or more, mechanical properties such as strength and elongation percentage of the fiber can be improved by drawing. Therefore, it is preferable that the drawing rate be 1.02 or more. The drawing rate is more preferably 1.2 times or more, further preferably 1.5 times or more. When the drawing rate is 7.0 times or less, yarn breakage during drawing is suppressed, and drawing can be stably performed. Therefore, it is preferable that the drawing rate be 7.0 times or less. The drawing rate is more preferably 6.0 times or less, further preferably 5.0 times or less.

When drawing is performed, the drawing speed may be appropriately selected depending on drawing methods such as the one-step process or the two-step process. In the one-step process, the speed of the high speed roller of the above-mentioned spinning speed corresponds to the drawing speed. When the drawing is performed in the two-step process, the drawing speed is preferably 30 to 1,000 m/min. When the drawing speed is 30 m/min or more, the traveling yarn is stabilized, and yarn breakage can be suppressed. Therefore, it is preferable that the drawing speed be 30 m/min or more. When the drawing is performed in the two-step process, the drawing speed is more preferably 50 m/min or more, further preferably 100 m/min or more. When the drawing speed is 1,000 m/min or less, yarn breakage during drawing is suppressed, and drawing can be stably performed. Therefore, it is preferable that the drawing speed be 1,000 m/min or less. When the drawing is performed in the two-step process, the drawing speed is more preferably 900 m/min or less, further preferably 800 m/min or less.

When false twisting processing is performed, a so-called buleria processing in which both a one-stage heater and a two-stage heater are used can be appropriately selected in addition to a so-called woolie finish in which only a one-stage heater is used. The heating method of the heater may be a contact type or a non-contact type. Specific examples of the false twisting processing machine include, but are not limited to, a friction disc type machine, a belt nip type machine, and a pin type machine.

When the false twisting processing is performed, the temperature of the heater may be appropriately selected depending on the extrapolated melting onset temperature of the polymers of the sea component and the island component and the like, but it is preferably 120 to 210° C. When the temperature of the heater is 120° C. or more, the preheating of the yarn supplied for the false twisting processing is sufficiently performed, thermal deformation due to drawing is uniform, generation of unevenness of fineness can be suppressed, dyeing specks and/or fluffs are small, and thus the quality is good. Therefore, it is preferable that the temperature of the heater be 120° C. or more. The temperature of the heater is more preferably 140° C. or more, further preferably 160° C. or more. When the temperature of the heater is 210° C. or less, fusion between fibers and thermal decomposition due to the contact with the heating heater is suppressed. Thus, yarn breakage and dirt in the heating heater are small, and the process passability and quality are good. Therefore, it is preferable that the temperature of the heater be 210° C. or less. The temperature of the heater is more preferably 200° C. or less, further preferably 190° C. or less.

When the false twisting processing is performed, the drawing rate may be appropriately selected depending on the elongation percentage of the fiber before false twisting processing, the strength and the elongation percentage of the fiber after false twisting processing and the like, but it is preferably 1.01 to 2.5 times. When the drawing rate is 1.01 or more, mechanical properties such as strength and elongation percentage of the fiber can be improved by drawing. Therefore, it is preferable that the drawing rate be 1.01 or more. The drawing rate is more preferably 1.2 times or more, further preferably 1.5 times or more. When the drawing rate is 2.5 times or less, yarn breakage during false twisting processing is suppressed, and false twisting processing can be stably performed. Therefore, it is preferable that the drawing rate be 2.5 times or less. The drawing rate is more preferably 2.2 times or less, further preferably 2.0 times or less.

When the false twisting processing is performed, the processing speed may be appropriately selected, but it is preferably 200 to 1,000 m/min. When the processing speed is 200 m/min or more, the traveling yarn is stabilized, and yarn breakage can be suppressed. Therefore, it is preferable that the processing speed be 200 m/min or more. The processing speed is more preferably 300 m/min or more, further preferably 400 m/min or more. When the processing speed is 1,000 m/min or less, yarn breakage during false twisting processing is suppressed, and false twisting processing can be stably performed. Therefore, it is preferable that the processing speed be 1,000 m/min or less. The processing speed is more preferably 900 m/min or less, further preferably 800 m/min or less.

The fiber or the fiber structure can be dyed as needed. A disperse dye can be suitably employed as a dye.

The dyeing method is not particularly limited, and a cheese dyeing machine, a liquid flow dyeing machine, a drum dyeing machine, a beam dyeing machine, a jigger, a high-pressure jigger or the like can be suitably employed according to a known method.

The dye concentration and the dyeing temperature are not particularly limited, and a known method can be suitably employed. Scouring may be performed before the dyeing process, or reduction cleaning may be performed after the dyeing process as needed.

The sea-islands type composite fiber, and the false twist yarn and the fiber structure including the same are excellent in moisture absorbability. Therefore, they can be suitably used in applications requiring comfort and quality. Examples of the applications include, but are not limited to, general clothing applications, sports apparel applications, bedding applications, interior applications, and materials applications.

EXAMPLES

Hereinafter, our fibers, yarns, fiber structures and methods will be described in more detail with reference to Examples. Each characteristic value in the Examples was obtained by the following method.

A. Moisture Absorption Rate Difference (ΔMR) of Sea Component and Island Component

The polymer of the sea component or the island component as a sample was first dried with hot air at 60° C. for 30 minutes, allowed to stand in constant temperature and humidity chamber LHU-123 manufactured by ESPEC CORP. conditioned at a temperature of 20° C. and a humidity of 65% RH for 24 hours, and the weight of the polymer (W1) was measured. Then, the polymer was allowed to stand in the constant temperature and humidity chamber conditioned at a temperature of 30° C. and a humidity of 90% RH for 24 hours, and then the weight of the polymer (W2) was measured. Thereafter, the polymer was dried with hot air at 105° C. for 2 hours, and the weight of the polymer (W3) after absolute drying was measured. The moisture absorption rate MR1 (%) from the absolute dry condition to the condition after being allowed to stand under the atmosphere of a temperature of 20° C. and a humidity of 65% RH for 24 hours was calculated from the following formula using the weights of the polymer, W1 and W3, and the moisture absorption rate MR2 (%) from the absolute dry condition to the condition after being allowed to stand under the atmosphere of a temperature of 30° C. and a humidity of 90% RH for 24 hours was calculated from the following formula using the weights of the polymer, W2 and W3. Then, the moisture absorption rate difference (ΔMR) was calculated by the following formula. Measurement was performed 5 times per sample, and the average value was taken as the moisture absorption rate difference (ΔMR).

MR1(%)={(W1−W3)/W3}×100

MR2(%)={(W2−W3)/W3}×100

Moisture absorption rate difference (ΔMR) (%)=MR2−MR1.

B. Extrapolated Melting Onset Temperature

The extrapolated melting onset temperature was measured using differential scanning calorimeter (DSC) model Q2000 manufactured by TA Instruments, using the polymers of the sea component and the island component, and the fiber obtained according to Examples as a sample. First, about 5 mg of the sample was heated from 0° C. to 280° C. under a nitrogen atmosphere at a heating rate of 50° C./min, and then kept at 280° C. for 5 minutes to remove the thermal history of the sample. Then, the sample was rapidly cooled from 280° C. to 0° C., heated again from 0° C. to 280° C. at a heating rate of 3° C./min, a temperature modulation amplitude of ±1° C., and a temperature modulation period of 60 seconds, and TMDSC measurement was performed. According to JIS K 7121: 1987 (Testing Methods for Transition Temperatures of Plastics) 9.1, the extrapolated melting onset temperature was calculated from the melting peak observed during the second heating process. Measurement was performed 3 times per sample, and the average value was taken as the extrapolated melting onset temperature. When a plurality of melting peaks were observed, the extrapolated melting onset temperature was calculated from the melting peak at the lowest temperature.

C. Sea/Island Composite Ratio

The sea/island composite ratio (the weight ratio) was calculated from the weight of the sea component and the weight of the island component used as the raw material of the sea-islands type composite fiber.

D. Fineness

Under an environment of a temperature of 20° C. and a humidity of 65% RH, a skein of 100 m of the fiber obtained according to Examples was obtained using an electric measuring machine manufactured by INTEC Inc. The weight of the obtained skein was measured, and the fineness (dtex) was calculated using the following formula. The measurement was carried out 5 times per sample, and the average value was taken as the fineness.

Fineness (dtex)=weight (g) of 100 m of fiber×100.

E. Strength and Elongation Percentage

The strength and elongation percentage were calculated according to JIS L 1013: 2010 (Testing methods for man-made filament yarns) 8.5.1 using the fiber obtained in Examples as a sample. Tension test was performed under the conditions of an initial sample length of 20 cm and a tension rate of 20 cm/min using Tensilon UTM-III-100 manufactured by ORIENTEC co., LTD under an environment of a temperature of 20° C. and a humidity of 65% RH. The strength (cN/dtex) was calculated by dividing the stress (cN) at the point showing the maximum load by the fineness (dtex), and the elongation percentage (%) was calculated by the following formula using the elongation (L1) at the point showing the maximum load and the initial sample length (L0). Measurement was carried out ten times per sample, and the average value was taken as the strength and the elongation percentage.

Elongation percentage (%)={(L1−L0)/L0}×100.

F. Diameter R of Fiber

The fiber obtained according to Examples was embedded in epoxy resin, frozen by FC·4E cryo sectioning system manufactured by Reichert, Inc., and cut with Reichert-Nissei ultracut N (ultramicrotome) equipped with a diamond knife. Thereafter, the cut surface, that is, the transverse cross section of the fiber was observed at a magnification of 1,000 using transmission electron microscope (TEM) H-7100FA model manufactured by Hitachi, Ltd., and a micrograph of the transverse cross section of the fiber was taken. Ten single yarns were randomly extracted from the obtained photograph, the diameters of the fiber of all extracted single yarns were measured using image processing software (WINROOF manufactured by MITANI CORPORATION), and the average value was taken as the diameter R of the fiber (nm). The transverse cross section of the fiber was not necessarily a perfect circle. Thus, when the transverse cross section of the fiber was not a perfect circle, the diameter of the circumscribed circle of the transverse cross section of the fiber was taken as the diameter of the fiber.

G. Thickness T of Outermost Layer

The transverse cross section of the fiber was observed in the same manner as in the diameter of the fiber described in F above, and a micrograph was taken at the highest magnification that allows the observation of the entire image of the single yarn. In the obtained photograph, using the image processing software (WINROOF manufactured by MITANI CORPORATION), the radius of the perfect circle in contact with the outline of the transverse cross section of the fiber at two or more points is determined as the radius of the fiber. Further, the radius of the perfect circle (the circumscribed circle) circumscribing two or more island components disposed in the outer circumference of the sea-island structure, as shown in 4 in FIG. 1(a), was determined. Ten single yarns were randomly extracted from the obtained photograph, and the radius of the fiber and the radius of the circumscribed circle of the sea-island structure portion were determined in the same manner. Then, the difference between the radius of the fiber and the radius of the circumscribed circle of the sea-island structure portion was calculated in each single yarn, and the average value was taken as the thickness T of the outermost layer (nm).

H. T/R

T/R was calculated by dividing the thickness T of the outermost layer (nm) calculated in G above by the diameter R of the fiber (nm) calculated in F above.

I. Diameter r, r1, and r2 of Island Component

The transverse cross section of the fiber was observed in the same manner as in the diameter of the fiber described in F above, and a micrograph was taken at the highest magnification that allows the observation of the entire image of the single yarn. In the obtained photograph, the diameters of all the island components in the transverse cross section of the fiber were measured using the image processing software (WINROOF manufactured by MITANI CORPORATION). The island component was not necessarily a perfect circle. Thus, when the island component was not a perfect circle, the diameter of the circumscribed circle of the island component was taken as the diameter of the island component. In the transverse cross section of the fiber, the average value of the diameters of all the island components was calculated as r, the diameter of the island component passing through the center was calculated as r1, and the average value of the diameters of all the island components except the island component passing through the center was calculated as r2. Ten single yarns were randomly extracted from the obtained photograph, r, r1, and r2 were determined in the same manner in each single yarn, and the average values were taken as r (nm), r1 (nm), and r2 (nm).

J. r1/r2

r1/r2 was calculated by dividing r1 (nm) calculated in I above by r2 (nm) calculated in I above.

K. Moisture Absorption Rate Difference (ΔMR) After Scouring and After Hot Water Treatment

Approximately 2 g of tubular knitting was prepared using the fiber obtained according to Examples as a sample using circular knitting machine NCR-BL manufactured by EIKO INDUSTRIAL CO., LTD. (caliber: 3 inch half (8.9 cm), 27 gauges), then scoured at 80° C. for 20 minutes in an aqueous solution containing 1 g/L of sodium carbonate and surfactant SUNMORL BK-80 manufactured by NICCA CHEMICAL CO., LTD., and dried at 60° C. for 60 minutes in a hot air dryer to obtain the tubular knitting after scouring. The tubular knitting after scouring was subjected to a hot water treatment under the conditions of a bath ratio of 1:100, a treatment temperature of 130° C., and a treatment time of 60 minutes, and then dried in a hot air dryer at 60° C. for 60 minutes to obtain the tubular knitting after a hot water treatment.

The moisture absorption rate (%) was calculated according to the moisture percentage of JIS L 1096: 2010 (Testing methods for woven and knitted fabrics) 8.10 using the tubular knitting after scouring and the tubular knitting after a hot water treatment as samples. First, the tubular knitting was dried with hot air at 60° C. for 30 minutes, then allowed to stand in constant temperature and humidity chamber LHU-123 manufactured by ESPEC CORP. conditioned at a temperature of 20° C. and a humidity of 65% RH for 24 hours, and the weight of the tubular knitting (W1) was measured. Then, the tubular knitting was allowed to stand in the constant temperature and humidity chamber conditioned at a temperature of 30° C. and a humidity of 90% RH for 24 hours, and the weight of the tubular knitting (W2) was measured. Thereafter, the tubular knitting was dried with hot air at 105° C. for 2 hours, and the weight of the tubular knitting (W3) after absolute drying was measured. The moisture absorption rate MR1 (%) from the absolute dry condition to the condition after being allowed to stand under the atmosphere of a temperature of 20° C. and a humidity of 65% RH for 24 hours was calculated from the following formula using the weights of the tubular knitting, W1 and W3, and the moisture absorption rate MR2 (%) from the absolute dry condition to the condition after being allowed to stand under the atmosphere of a temperature of 30° C. and a humidity of 90% RH for 24 hours was calculated from the following formula using the weights of the tubular knitting, W2 and W3. Then, the moisture absorption rate difference (ΔMR) was calculated by the following formula. Measurement was performed 5 times per sample, and the average value was taken as the moisture absorption rate difference (ΔMR).

MR1(%)={(W1−W3)/W3}×100

MR2(%)={(W2−W3)/W3}×100

Moisture absorption rate difference (ΔMR) (%)=MR2−MR1.

L. Cracks of Sea Component

The tubular knitting after a hot water treatment produced in K above was vapor-deposited with a platinum-palladium alloy, and observed at a magnification of 1,000 using scanning electron microscope (SEM) S-4000 manufactured by Hitachi, Ltd., and micrographs of 10 fields were randomly taken. In the obtained 10 micrographs, the total of the places where the sea component is cracked was taken as the cracks (the places) of the sea component.

M. L* Value

The tubular knitting after scouring produced in the same manner as in K above was subjected to dry heat setting at 160° C. for 2 minutes, and the tubular knitting after dry heat setting was dyed under the conditions of a bath ratio of 1:100, a dyeing temperature of 130° C., a dyeing time of 60 minutes in a dyeing solution to which 1.3% by weight of Kayalon Polyester Blue UT-YA manufactured by Nippon Kayaku Co., Ltd. as a disperse dye was added and which was adjusted to pH 5.0. When a cation dyeable polyester was used as the sea component, the knitting was dyed under the conditions of a bath ratio of 1:100, a dyeing temperature of 130° C., a dyeing time of 60 minutes in a dyeing solution to which 1.0% by weight of Kayacryl Blue 2RL-ED manufactured by Nippon Kayaku Co., Ltd. as a cationic dye was added and which was adjusted to pH 4.0.

Using the tubular knitting after dyeing as a sample, L* value was measured under the conditions of D65 light source, a viewing angle of 10°, and an optical condition of SCE (Specular Component Exclude) using spectrophotometer CM-3700d model manufactured by KONICA MINOLTA JAPAN, INC. The measurement was carried out three times per sample, and the average value was taken as the L* value.

N. Leveling

Five inspectors having experience of quality judgment of 5 years or more discussed and determined the leveling of the tubular knitting after dyeing produced in M above as follows: “the knitting that is very levelly dyed and has no dyeing specks confirmed” was determined as S, “the knitting that is almost levelly dyed and has almost no dyeing specks confirmed” was determined as A, “the knitting that is almost not levelly dyed and has slight dyeing specks confirmed” was determined as B, and “the knitting that is not levelly dyed and has clear dyeing specks confirmed” was determined as C. A and S were defined as acceptable levels.

O. Quality

Five inspectors having experience of quality judgment of 5 years or more discussed and determined the quality of the tubular knitting after dyeing produced in M above as follows: “the knitting that has no fluffs and has extremely excellent quality” was determined as S, “the knitting that has almost no fluffs and has excellent quality” was determined as A, “the knitting that has fluffs and has poor quality” was determined as B, and “the knitting that has many fluffs and has extremely poor quality” was determined as C. A and S were defined as acceptable levels.

P. Dry Touch

Five inspectors having experience of quality judgment of 5 years or more discussed and determined the dry touch of the tubular knitting after dyeing produced in M above as follows: “the knitting that has no slime or stickiness and has extremely excellent dry touch” was determined as S, “the knitting that has almost no slime or stickiness and has excellent dry touch” was determined as A, “the knitting that has slime or stickiness and has poor dry touch” was determined as B, and “the knitting that has strong slime or stickiness and has extremely poor dry touch” was determined as C. A and S were defined as acceptable levels.

Example 1

Polyethylene terephthalate copolymerized with 30% by weight of polyethylene glycol having a number average molecular weight of 8,300 g/mol (PEG 6000S manufactured by Sanyo Chemical Industries, Ltd.) as an island component, and polyethylene terephthalate (IV=0.66) as a sea component were each vacuum dried at 150° C. for 12 hours, then separately supplied and melted in a extruder type composite spinning machine at a compounding ratio of 30% by weight of the island component and 70% by weight of the sea component, poured into the spinning pack having the sea-island composite spinneret shown in FIG. 2(a) incorporated therein at a spinning temperature of 285° C., and a composite polymer flow was discharged from the discharge hole at a discharge rate of 25 g/min to obtain a spun yarn. The distribution plate on the discharge plate used had 18 distribution holes drilled per one discharge hole for the island component. The annular groove used for the sea component, as shown in 16 of FIG. 3, had distribution holes drilled every 1° in the circumferential direction. The discharge loading hole length was 5 mm, the reduction hole angle was 60°, the discharge hole diameter was 0.18 mm, the discharge hole length/discharge hole diameter was 2.2, and the discharge hole number was 72. The spun yarn was cooled with cooling air at a wind temperature of 20° C. and a wind speed of 20 m/min. An oil agent was applied to the yarn by an oiling device to converge the yarn. The yarn was taken up by a first godet roller rotating at 2,700 m/min, and wound by a winder through a second godet roller rotating at the same speed as the first godet roller to obtain an undrawn yarn of 92 dtex-72 f. Thereafter, the obtained undrawn yarn was drawn and false twisted under the conditions of the temperature of the heater of 140° C. and a rate of 1.4 times using a drawing and false twisting machine (the twisting portion: a friction disc type, the heater portion: a contact type) to obtain a false twist yarn of 66 dtex-72 f.

The evaluation results of the fiber properties and fabric properties of the obtained fiber are shown in Table 1. Although there was a slight number of cracks of the sea component, the moisture absorbability reduction due to the hot water treatment was little, and the moisture absorbability was good even after the hot water treatment. The coloring was also good, and the leveling, quality, and dry touch were all at acceptable levels.

Examples 2 to 5 and Comparative Example 1

A false twist yarn was produced in the same manner as in Example 1 except that the ratio (T/R) of a thickness T of an outermost layer to a diameter R of the fiber was changed as shown in Table 1.

The evaluation results of the fiber properties and fabric properties of the obtained fiber are shown in Table 1. In Examples 2 to 5, as T/R increased, the cracks of the sea component decreased, and the coloring improved. Meanwhile, the moisture absorbability after the hot water treatment was decreased, but the moisture absorbability was good. In all instances, the leveling, quality, and dry touch were all at acceptable levels. Meanwhile, in Comparative Example 1, though the coloring, leveling, quality, and dry touch were good, both the moisture absorbability after the scouring and the moisture absorbability after the hot water treatment were low. This is because T/R was large, and thus the volume expansion of the moisture absorbing polymer of the island component was suppressed.

Comparative Example 2

A false twist yarn was produced in the same manner as in Example 1 except that a conventionally known pipe sea-island composite spinneret (18 islands per discharge hole) described in Japanese Patent Laid-open Publication No. 2007-100243 was used.

The evaluation results of the fiber properties and fabric properties of the obtained fiber are shown in Table 1. When the conventionally known pipe sea-island composite spinneret was used, the thickness of the outermost layer of the obtained fiber was thin, and thus the cracks of the sea component upon the volume expansion of the moisture absorbing polymer of the island component during the hot water treatment was extremely large. Due to the cracks of the sea component, the moisture absorbing polymer of the island component eluted during the hot water treatment, the moisture absorbability greatly reduced after the hot water treatment, and the moisture absorbability was poor. Many dyeing specks and/or fluffs caused by the cracks of the sea component were observed, and the leveling and quality were extremely poor. Further, due to the cracks of the sea component, a part of the moisture absorbing polymer of the island component was exposed on the surface, thus there was slime and stickiness, and the dry touch was poor.

Comparative Example 3

A false twist yarn was produced in the same manner as in Example 1 except that a core-sheath composite spinneret was used. In Comparative Example 3, the sea component and the island component described in Table 1 correspond to the sheath component and the core component, respectively.

The evaluation results of the fiber properties and fabric properties of the obtained fiber are shown in Table 1. The cracks of the sheath component upon the volume expansion of the moisture absorbing polymer of the core component during the hot water treatment was extremely large. Due to the cracks of the sheath component, the moisture absorbing polymer of the core component eluted during the hot water treatment, the moisture absorbability greatly reduced after the hot water treatment, and the moisture absorbability was poor. Many dyeing specks and/or fluffs caused by the cracks of the sheath component were observed, and the leveling and quality were extremely poor. Further, due to the cracks of the sheath component, a part of the moisture absorbing polymer of the core component was exposed on the surface, thus there was slime and stickiness, and the dry touch was poor.

Examples 6 to 11

A false twist yarn was produced in the same manner as in Example 1 except that the number and disposition of the island component were changed as shown in Table 2 in the distribution plate of the sea-island composite spinneret described in Example 1.

The evaluation results of the fiber properties and fabric properties of the obtained fiber are shown in Table 2. Though the number and disposition of the island component were changed, the number of the cracks of the sea component was small, and the moisture absorbability after the hot water treatment was also good. The coloring was also good, and the leveling, quality, and dry touch were all at acceptable levels.

Examples 12 to 15

A false twist yarn was prepared in the same manner as in Example 9 except that the sea/island composite ratio was changed as shown in Table 3.

The evaluation results of the fiber properties and fabric properties of the obtained fiber are shown in Table 3. In all the sea/island composite ratios, the number of the cracks of the sea component was small, and the moisture absorbability after the hot water treatment, coloring, leveling, quality, and dry touch were all good.

Examples 16 to 18

A false twist yarn was produced in the same manner as in Example 1 except that, in the distribution plate of the sea-island composite spinneret described in Example 1, the shape of the island component was changed to a hexagon as shown in FIG. 1(h) in Example 16, and a trefoil as shown in FIG. 1(i) in Example 17, and the shape of the center side of the island component disposed in the outermost circle in the transverse cross section of the fiber was changed to a non-circular shape as shown in FIG. 1(j) in Example 18.

The evaluation results of the fiber properties and fabric properties of the obtained fiber are shown in Table 3. Though the shape of the island component was changed, the number of the cracks of the sea component was small, and the moisture absorbability after the hot water treatment, coloring, leveling, quality, and dry touch were all good. In particular, in Example 18, in the island component disposed in the outermost circle, the fiber internal side was non-circular, thus the stress was concentrated not on the fiber surface side but on the non-circular portion, and the propagation of breaks to the fiber surface was blocked, thereby the effect of suppressing the cracks of the sea component was excellent.

Examples 19 to 23

A false twist yarn was produced in the same manner as in Example 1 except that, in the distribution plate of the sea-island composite spinneret described in Example 1, the number and disposition of the island component were changed, and the ratio (r1/r2) of a diameter r1 of the island component disposed to pass through a center of the transverse cross section of the fiber to a diameter r2 of other island components was changed as shown in Table 4.

The evaluation results of the fiber properties and fabric properties of the obtained fiber are shown in Table 4. As r1/r2 increased, the cracks of the sea component decreased, and the coloring was improved, while the moisture absorbability after the hot water treatment decreased. However, the moisture absorbability was good. In all instances, the leveling, quality, and dry touch were all at acceptable levels.

Examples 24 to 26 and Comparative Examples 4 and 5

A false twist yarn was prepared in the same manner as in Example 9 except that the number average molecular weight and the copolymerization ratio of polyethylene glycol, the copolymerization component of the island component were changed as shown in Table 5.

The evaluation results of the fiber properties and fabric properties of the obtained fiber are shown in Table 5. Though the number average molecular weight and the copolymerization ratio of polyethylene glycol were changed in Examples 24 to 26, the number of the cracks of the sea component was small, and the moisture absorbability after the hot water treatment, coloring, leveling, quality, and dry touch were all good. Meanwhile, in Comparative Examples 4 and 5, though there was no crack of the sea component and the coloring, leveling, and dry touch were good, the moisture absorbability of the moisture absorbing polymer of the island component was low. Thus, both the moisture absorbability after the scouring and the moisture absorbability after the hot water treatment were low, and the moisture absorbability was extremely poor.

Examples 27 and 28

A false twist yarn was prepared in the same manner as in Example 9 except that the island component was changed to polybutylene terephthalate copolymerized with polyethylene glycol at the number average molecular weight and the copolymerization ratio as shown in Table 6.

The evaluation results of the fiber properties and fabric properties of the obtained fiber are shown in Table 6. Though the polybutylene terephthalate copolymerized with polyethylene glycol was used as the island component, the number of the cracks of the sea component was small, and the moisture absorbability after the hot water treatment, coloring, leveling, quality, and dry touch were all good.

Examples 29 and 30

A false twist yarn was prepared in the same manner as in Example 9 except that the island component was changed to nylon 6 copolymerized with 30% by weight of polyethylene glycol having a number average molecular weight of 3,400 g/mol (PEG 40005 manufactured by Sanyo Chemical Industries, Ltd.) in Example 29, and “PEBAX MH 1657” manufactured by Arkema in Example 30.

The evaluation results of the fiber properties and fabric properties of the obtained fiber are shown in Table 6. Though polyether amide was used as the island component, the number of the cracks of the sea component was small, and the moisture absorbability after the hot water treatment, coloring, leveling, quality, and dry touch were all good.

Example 31

A false twist yarn was prepared in the same manner as in Example 9 except that the island component was changed to “PAS-40N” manufactured by TORAY INDUSTRIES, INC.

The evaluation results of the fiber properties and fabric properties of the obtained fiber are shown in Table 6. Though polyetherester amide was used as the island component, the number of the cracks of the sea component was small, and the moisture absorbability after the hot water treatment, coloring, leveling, quality, and dry touch were all good.

Examples 32, 33

A false twist yarn was produced in the same manner as in Example 19 except that the sea component was changed to polyethylene terephthalate (IV=0.66) copolymerized with 1.5% by mole of 5-sulfoisophthalic acid sodium salt and 1.0% by weight of polyethylene glycol having a number average molecular weight of 1,000 g/mol (PEG 1,000 manufactured by Sanyo Chemical Industries, Ltd.) in Example 32, and polybutylene terephthalate (IV=0.66) in Example 33.

The evaluation results of the fiber properties and fabric properties of the obtained fiber are shown in Table 7. Though a cation dyeable polyester was used in Example 32, and polybutylene terephthalate was used in Example 33 as the sea component, the number of the cracks of the sea component was small, and the moisture absorbability after the hot water treatment, coloring, leveling, quality, and dry touch were all good.

Examples 34 to 37

A false twist yarn was produced in the same manner as in Example 19 except that the discharge rate was changed to 32 g/min and the number of the discharge hole of the sea-island composite spinneret was changed to 24 in Example 34, the discharge rate was changed to 32 g/min and the number of the discharge hole of the sea-island composite spinneret was changed to 48 in Example 35, the discharge rate was changed to 32 g/min in Example 36, and the discharge rate was changed to 38 g/min in Example 37. A false twist yarn of 84 dtex-24f was obtained in Example 34, a false twist yarn of 84 dtex-48f was obtained in Example 35, a false twist yarn of 84 dtex-72f was obtained in Example 36, and a false twist yarn of 100 dtex-72f was obtained in Example 37.

The evaluation results of the fiber properties and fabric properties of the obtained fiber are shown in Table 7. Though the fineness and the single yarn fineness were changed, the number of the cracks of the sea component was small, and the moisture absorbability after the hot water treatment, coloring, leveling, quality, and dry touch were all good.

Comparative Example 6

A false twist yarn was produced in the same manner as in Example 1 except that the spinneret was changed to a spinneret for single component (the number of the hole: 72, round holes) and only the moisture absorbing polymer was used for spinning, drawing, and false twisting.

The evaluation results of the fiber properties and fabric properties of the obtained fiber are shown in Table 8. Because the fiber was composed of only the moisture absorbing polymer, the moisture absorbability after the hot water treatment was high. However, the discharge from the spinneret was unstable, many of the obtained fiber had thick parts and thin parts, the strength was low, many dyeing specks and/or fluffs were observed, and the leveling and quality were extremely poor. Further, because the moisture absorbing polymer was exposed on the fiber surface, there was slime and stickiness, and the dry touch was extremely poor.

Comparative Example 7

A false twist yarn was produced in the same manner as in Example 19 except that the sea component and the island component in Example 19 were interchanged and the sea/island composite ratio was changed to 30/70.

The evaluation results of the fiber properties and fabric properties of the obtained fiber are shown in Table 8. There was no crack of the sea component and the moisture absorbability after the hot water treatment and coloring are good. However, the moisture absorbing polymer of the sea component was exposed on the fiber surface, and thus there were slime and stickiness, and the dry touch was extremely poor. Also, the leveling and quality were also not at acceptable levels.

Comparative Example 8

A false twist yarn was produced in the same manner as in Example 32 except that the island component was changed to polyethylene terephthalate (IV=0.66).

The evaluation results of the fiber properties and fabric properties of the obtained fiber are shown in Table 8. There was no crack of the sea component, and the coloring, leveling, quality, and dry touch were good. However, the moisture absorbability was extremely poor, because both the sea component and the island component were not moisture absorbing polymers.

Example 38

A false twist yarn was prepared in the same manner as in Example 9 except that the island component was changed to polyethylene terephthalate copolymerized with 35% by weight of polyethylene glycol having a number average molecular weight of 8,300 g/mol (PEG 6000S manufactured by Sanyo Chemical Industries, Ltd.) and 19% by weight of ethylene oxide adduct of bisphenol A [m+n=4] (NEWPOL BPE-40 manufactured by Sanyo Chemical Industries, Ltd.).

The evaluation results of the fiber properties and fabric properties of the obtained fiber are shown in Table 9. Though the polyethylene terephthalate copolymerized with polyethylene glycol and ethylene oxide adduct of bisphenol A was used as the island component, the number of the cracks of the sea component was small, and the moisture absorbability after the hot water treatment, coloring, leveling, quality, and dry touch were all good.

Examples 39 to 41

A false twist yarn was prepared in the same manner as in Example 38 except that “m+n” of ethylene oxide adduct of bisphenol A, the copolymerization component of the island component in Example 38, and the copolymerization ratio were changed as shown in Table 9.

The evaluation results of the fiber properties and fabric properties of the obtained fiber are shown in Table 9. Though “m+n” of ethylene oxide adduct of bisphenol A and the copolymerization ratio were changed, the number of the cracks of the sea component was small, and the moisture absorbability after the hot water treatment, coloring, leveling, quality, and dry touch were all good.

Examples 42, 43

A false twist yarn was prepared in the same manner as in Example 40 except that the copolymerization ratio of polyethylene glycol, the copolymerization component of the island component in Example 40 was changed as shown in Table 10.

The evaluation results of the fiber properties and fabric properties of the obtained fiber are shown in Table 10. Though the copolymerization ratio of polyethylene glycol was changed, the number of the cracks of the sea component was small, and the moisture absorbability after the hot water treatment, coloring, leveling, quality, and dry touch were all good.

Examples 44, 45

A false twist yarn was prepared in the same manner as in Example 38 except that the number average molecular weight of polyethylene glycol, the copolymerization component of the island component in Example 38 was changed as shown in Table 10.

The evaluation results of the fiber properties and fabric properties of the obtained fiber are shown in Table 10. Though the number average molecular weight of polyethylene glycol was changed, the number of the cracks of the sea component was small, and the moisture absorbability after the hot water treatment, coloring, leveling, quality, and dry touch were all good.

TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Production Sea Polymer type PET PET PET PET PET conditions component Moisture absorption rate difference (ΔMP) [%] 0.1 0.1 0.1 0.1 0.1 Extrapolated melting onset temperature [° C.] 239 239 239 239 239 Island Polymer type Polyether Polyether Polyether Polyether Polyether component ester ester ester ester ester Polyether type PEG PEG PEG PEG PEG Number average molecular werght of polyether [g/mol] 8300 8300 8300 8300 8300 Copolymerization ratio of polyether [% by weight] 30 30 30 30 30 Moisture absorption rate difference (ΔMP) [%] 11.0 11.0 11.0 11.0 11.0 Extrapolated melting onset temperature [° C.] 236 236 236 236 236 Sea/Island composite ratio [weight ratio] 70/30 70/30 70/30 70/30 70/30 Cross-sectional shape FIG. 1 (a) FIG. 1 (a) FIG. 1 (a) FIG. 1 (a) FIG. 1 (a) Number of islands [pieces] 18 18 18 18 18 Disposition of islands [circles] 2 2 2 2 2 Fiber Fineness [dtex] 66 66 66 66 66 properties Strength [cN/dtex] 2.2 2.4 2.5 2.6 2.6 Elongation percentage [%] 36 38 39 37 38 Extrapolated melting onset temperature [° C.] 236 236 236 236 236 Diameter R of fiber [nm] 9158 9057 9184 9155 9229 Thickness T of outermost layer [nm] 475 720 1030 1935 2125 T/R 0.052 0.079 0.112 0.211 0.230 Diameter r of island component [nm] 1202 1194 1173 1224 1185 Diameter r1 of island component [nm] — — — — — Diameter r2 of island component [nm] 1202 1194 1173 1224 1185 r1/r2 — — — — — Fabric Moisture absorption rate difference after scouring (ΔMR) [%] 3.1 3.1 3.0 2.7 2.5 properties Moisture absorption rate difference after hot water treatment (ΔMR) [%] 2.8 3.0 2.9 2.6 2.4 Cracks of sea component [places] 9 5 3 1 0 L* value 33 27 24 23 23 Leveling A A S S S Quality A S S S S Dry touch S S S S S Comparative Comparative Comparative Example 1 Example 2 Example 3 Production Sea Polymer type PET PET PET conditions component Moisture absorption rate difference (ΔMR) [%] 0.1 0.1 0.1 Extrapolated melting onset temperature [° C.] 239 239 239 Island Polymer type Polyether Polyether Polyether component ester ester ester Polyether type PEG PEG PEG Number average molecular weight of polyether [g/mol] 8300 8300 8300 Copolymerization ratio of polyether [% by weight] 30 30 30 Moisture absorption rate difference (ΔMR) [%] 11.0 11.0 11.0 Extrapolated melting onset temperature [° C] 236 236 236 Sea/Island composite ratio [weight ratio] 70/30 70/30 70/30 Cross-sectional shape FIG. 1 (a) FIG. 1 (a) — Number of islands [pieces] 18 18 1 Disposition of islands [circles] 2 2 1 Fiber Fineness [dtex] 66 66 66 properties Strength [cN/dtex] 2.7 1.8 2.4 Elongation percentage [%] 39 33 33 Extrapolated melting onset temperature [° C.] 236 236 236 Diameter R of fiber [nm] 9325 9212 9202 Thickness T of outermost layer [nm] 2343 153 1581 T/R 0.251 0.017 0.172 Diameter r of island component [nm] 1152 1189 5037 Diameter r1 of island component [nm] — — 5037 Diameter r2 of island component [nm] 1152 1189 — r1/r2 — — — Fabric Moisture absorption rate difference after scouring (ΔMR) [%] 1.9 3.2 2.8 properties Moisture absorption rate difference after hot water treatment (ΔMR) [%] 1.8 1.3 1.2 Cracks of sea component [places] 0 47 43 L* value 22 41 25 Leveling S C C Quality S C C Dry touch S B B PET: polyethylene terephthalate, PEG: polyethylene glycol

TABLE 2 Example 6 Example 7 Example 8 Example 9 Example 10 Example 11 Production Sea Polymer type PET PET PET PET PET PET conditions component Moisture absorption rate difference (ΔMR) [%] 0.1 0.1 0.1 0.1 0.1 0.1 Extrapolated melting onset temperature [° C.] 239 239 239 239 239 239 Island Polymer type Polyether Polyether Polyether Polyether Polyether Polyether component ester ester ester ester ester ester Polyether type PEG PEG PEG PEG PEG PEG Number average molecular weight of 8300 8300 8300 8300 8300 8300 polyether [g/mol] Copolymerization ratio of polyether [% by weight] 30 30 30 30 30 30 Moisture absorption rate difference (ΔMR) [%] 11.0 11.0 11.0 11.0 11.0 11.0 Extrapolated melting onset temperature [° C.] 236 236 236 236 236 236 Sea/Island composite ratio [weight ratio] 70/30 70/30 70/30 70/30 70/30 70/30 Cross-sectional shape FIG. 1 (b) FIG. 1 (c) FIG. 1 (k) FIG. 1 (e) FIG. 1 (f) — Number of islands [pieces] 2 3 6 24 128 1024 Disposition of islands [circles] 1 1 2 3 7 12 Fiber Fineness [dtex] 66 66 66 66 66 66 properties Strength [cN/dtex] 2.4 2.5 2.4 2.5 2.6 2.7 Elongation percentage [%] 36 36 37 38 40 39 Extrapolated melting onset temperature [° C.] 236 236 236 236 236 236 Diameter R of fiber [nm] 9194 9279 9068 9265 9163 9270 Thickness T of outermost layer [nm] 1012 1055 1048 1061 1024 1007 T/R 0.110 0.114 0.116 0.115 0.112 0.109 Diameter r of island component [nm] 3421 2908 1989 1028 445 157 Diameter r1 of island component [nm] — — 2005 — — — Diameter r2 of island component [nm] 3421 2908 1986 1028 445 157 r1/r2 — — 1.01 — — — Fabric Moisture absorption rate difference after scouring (ΔMR) [%] 2.9 2.9 3.0 3.0 3.1 3.2 properties Moisture absorption rate difference after hot 2.4 2.5 2.9 2.9 3.0 3.1 water treatment (ΔMR) [%] Cracks of sea component [places] 17 11 5 2 1 0 L* value 26 24 25 24 23 24 Leveling A A A S S S Quality A A S S S S Dry touch A S S S S S PET: polyethylene terephthalate, PEG: polyethylene glycol

TABLE 3 Example Example Example Example Example Example Example 12 13 14 15 16 17 18 Production Sea Polymer type PET PET PET PET PET PET PET conditions component Moisture absorption rate 0.1 0.1 0.1 0.1 0.1 0.1 0.1 difference (ΔMR) [%] Extrapolated melting 239 239 239 239 239 239 239 onset temperature [° C.] Island Polymer type Polyether Polyether Polyether Polyether Polyether Polyether Polyether component ester ester ester ester ester ester ester Polyether type PEG PEG PEG PEG PEG PEG PEG Number average molecular 8300 8300 8300 8300 8300 8300 8300 weight of polyether [g/mol] Copolymerization ratio 30 30 30 30 30 30 30 of polyether [% by weight] Moisture absorption rate 11.0 11.0 11.0 11.0 11.0 11.0 11.0 difference (ΔMR) [%] Entrapolated melting onset 236 236 236 236 236 236 236 temperature [° C.] Sea/Island composite ratio [weight ratio] 45/55 50/50 60/40 80/20 70/30 70/30 70/30 Cross-sectional shape FIG. 1 (e) FIG. 1 (e) FIG. 1 (e) FIG. 1 (e) FIG. 1 (h) FIG. 1 (i) FIG. 1 (j) Number of islands [pieces] 24 24 24 24 18 18 18 Disposition of islands [circles] 3 3 3 3 2 2 2 Fiber Fineness [dtex] 66 66 66 66 66 66 66 properties Strength [cN/dtex] 2.0 2.2 2.4 2.7 2.5 2.4 2.6 Elongation percentage [%] 36 35 38 39 36 37 39 Entrapolated melting onset temperature 236 236 236 236 236 236 236 [° C.] Diameter R of fiber [nm] 9312 9292 9286 9232 9315 9301 9277 Thickness T of outermost layer [nm] 491 635 1036 1059 1095 1042 1138 T/R 0.053 0.068 0.112 0.115 0.118 0.112 0.123 Diameter r of island component [nm] 1345 1321 1187 840 1212 1243 1264 Diameter r1 of island component [nm] — — — — — — — Diameter r2 of island component [nm] 1345 1321 1187 840 1212 1243 1264 r1/r2 — — — — — — — Fabric Moisture absorption rate difference 5.5 5.1 4.0 2.2 3.0 3.0 3.0 properties after scouring (ΔMR) [%] Moisture absorption rate difference 5.0 4.7 3.8 2.1 2.9 2.9 2.9 after hot water treatment (ΔMR) [%] Cracks of sea component [places] 10 7 4 0 3 4 0 L* value 35 32 27 21 24 24 23 Leveling A A A S A A S Quality A A S S A A S Dry touch S S S S S S S PET: polyethylene terephthalate, PEG: polyethylene glycol

TABLE 4 Example 19 Example 20 Example 21 Example 22 Example 23 Production Sea Polymer type PET PET PET PET PET conditions component Moisture absorption rate difference (ΔMR) [%] 0.1 0.1 0.1 0.1 0.1 Extrapolated melting onset temperature [° C.] 239 239 239 239 239 Island Polymer type Polyether Polyether Polyether Polyether Polyether component ester ester ester ester ester Polyether type PEG PEG PEG PEG PEG Number average molecular weight of 8300 8300 8300 8300 8300 polyether [g/mol] Copolymerization ratio of polyether [% by weight] 30 30 30 30 30 Moisture absorption rate difference (ΔMR) [%] 11.0 11.0 11.0 11.0 11.0 Extrapolated melting onset temperature [° C.] 236 236 236 236 236 Sea/Island composite ratio [weight ratio] 70/30 70/30 70/30 70/30 70/30 Cross-sectional shape FIG. 1 (l) FIG. 1 (l) FIG. 1 (l) FIG. 1 (l) FIG. 1 (l) Number of islands [pieces] 18 18 18 18 18 Disposition of islands [circles] 3 3 3 3 3 Fiber Fineness [dtex] 66 66 66 66 66 properties Strength [cN/dtex] 2.5 2.6 2.7 2.7 2.8 Elongation percentage [%] 38 38 37 38 39 Extrapolated melting onset temperature [° C.] 236 236 236 236 236 Diameter R of fiber [nm] 9156 9355 9084 9177 9215 Thickness T of outermost layer [nm] 1033 1141 1072 1096 1127 T/R 0.113 0.122 0.118 0.119 0.122 Diameter r of island component [nm] — — — — — Diameter r1 of island component [nm] 1259 1708 2871 4104 4565 Diameter r2 of island component [nm] 1127 1029 845 675 498 r1/r2 1.12 1.66 3.40 6.08 9.17 Fabric Moisture absorption rate difference after scouring (ΔMR) [%] 3.0 2.9 2.9 2.8 2.7 properties Moisture absorption rate difference after hot water 2.9 2.8 2.8 2.7 2.6 treatment (ΔMR) [%] Cracks of sea component [places] 2 1 1 0 0 L* value 23 23 22 21 20 Leveling S S S S S Quality S S S S S Dry touch S S S S S PET: polyethylene terephthalate, PEG: polyethylene glycol

TABLE 5 Comparative Comparative Example 24 Example 25 Example 26 Example 4 Example 5 Production Sea Polymer type PET PET PET PET PET conditions component Moisture absorption rate difference (ΔMR) [%] 0.1 0.1 0.1 0.1 0.1 Extrapolated melting onset temperature [° C.] 239 239 239 239 239 Island Polymer type Polyether Polyether Polyether Polyether Polyether component ester ester ester ester ester Polyether type PEG PEG PEG PEG PEG Number average molecular weight of 3400 11000 20000 3400 8300 polyether [g/mol] Copolymerization ratio of polyether 55 20 20 15 5 [% by weight] Moisture absorption rate difference (ΔMR) [%] 17.5 6.8 7.5 1.4 0.4 Extrapolated melting onset temperature [° C.] 221 238 238 235 238 Sea/Island composite ratio [weight ratio] 70/30 70/30 70/30 70/30 70/30 Cross-sectional shape FIG. 1 (e) FIG. 1 (e) FIG. 1 (e) FIG. 1 (e) FIG. 1 (e) Number of islands [pieces] 24 24 24 24 24 Disposition of islands [circles] 3 3 3 3 3 Fiber Fineness [dtex] 66 66 66 66 66 properties Strength [cN/dtex] 2.1 2.5 2.6 2.4 2.9 Elongation percentage [%] 37 39 37 38 36 Extrapolated melting onset temperature [° C.] 221 238 238 235 238 Diameter R of fiber [nm] 9301 9251 9278 9315 9322 Thickness T of outermost layer [nm] 978 1023 1038 1011 1056 T/R 0.105 0.111 0.112 0.109 0.113 Diameter r of island component [nm] 1021 1037 1002 1016 985 Diameter r1 of island component [nm] — — — — — Diameter r2 of island component [nm] 1021 1037 1002 1016 985 r1/r2 — — — — — Fabric Moisture absorption rate difference after scouring 5.2 2.1 2.3 0.4 0.1 properties (ΔMR) [%] Moisture absorption rate difference after hot water 5.0 2.0 2.2 0.4 0.1 treatment (ΔMR) [%] Cracks of sea component [places] 2 2 0 0 L* value 24 23 24 21 19 Leveling S S S S S Quality S S S S S Dry touch S S S S S PET: polyethylene terephthalate, PEG: polyethylene glycol

TABLE 6 Example 27 Example 28 Example 29 Example 30 Example 31 Production Sea Polymer type PET PET PET PET PET conditions component Moisture absorption rate difference (ΔMR) [%] 0.1 0.1 0.1 0.1 0.1 Extrapolated melting onset temperature [° C.] 239 239 239 239 239 Island Polymer type Polyether Polyether Polyether Polyether Polyether component ester ester amide amide ester amide Polyether type PEG PEG PEG — — Number average molecular weight of 3400 8300 3400 — — polyether [g/mol] Copolymerization ratio of polyether 50 30 30 — — [% by weight] Moisture absorption rate difference (ΔMR) [%] 13.1 10.8 11.8 17.0 12.1 Extrapolated melting onset temperature [° C.] 185 208 194 179 155 Sea/Island composite ratio [weight ratio] 70/30 70/30 70/30 70/30 70/30 Cross-sectional shape FIG. 1 (e) FIG. 1 (e) FIG. 1 (e) FIG. 1 (e) FIG. 1 (e) Number of islands [pieces] 24 24 24 24 24 Disposition of islands [circles] 3 3 3 3 3 Fiber Fineness [dtex] 66 66 66 66 66 properties Strength [cN/dtex] 2.3 2.7 2.3 2.2 2.4 Elongation percentage [%] 38 36 37 38 37 Extrapolated melting onset temperature [° C.] 185 208 194 179 155 Diameter R of fiber [nm] 9317 9175 9114 9244 9358 Thickness T of outermost layer [nm] 986 1049 1004 991 1018 T/R 0.106 0.114 0.110 0.107 0.109 Diameter r of island component [nm] 1046 1054 995 1009 976 Diameter r1 of island component [nm] — — — — — Diameter r2 of island component [nm] 1046 1054 995 1009 976 r1/r2 — — — — — Fabric Moisture absorption rate difference after scouring 3.9 3.2 3.4 5.0 3.6 properties (ΔMR) [%] Moisture absorption rate difference after hot water 3.8 3.1 3.3 4.8 3.5 treatment (ΔMR) [%] Cracks of sea component [places] 3 2 4 4 2 L* value 25 24 28 29 27 Leveling S S A A S Quality S S S A S Dry touch S S S S S PET: polyethylene terephthalate, PEG: polyethylene glycol

TABLE 7 Example Example Example Example Example Example 32 33 34 35 36 37 Production Sea Polymer type Copolymerized PBT PET PET PET PET conditions component PET Polyether type — — — — — — Number average molecular — — — — — — weight of polyether [g/mol] Copolymerization ratio of — — — — — — polyether [% by weight] Moisture absorption rate 0.2 0.1 0.1 0.1 0.1 0.1 difference (ΔMR) [%] Extrapolated melting 233 211 239 239 239 239 onset temperature [° C.] Island Polymer type Polyether Polyether Polyether Polyether Polyether Polyether component ester ester ester ester ester ester Polyether type PEG PEG PEG PEG PEG PEG Number average molecular 8300 3400 8300 8300 8300 8300 weight of polyether [g/mol] Copolymerization ratio of 30 50 30 30 30 30 polyether [% by weight] Moisture absorption rate 11.0 13.1 11.0 11.0 11.0 11.0 difference (ΔMR) [%] Extrapolated melting 236 185 236 236 236 236 onset temperature [° C.] Sea/Island composite ratio [weight ratio] 70/30 70/30 70/30 70/30 70/30 70/30 Cross-sectional shape FIG. 1 (l) FIG. 1 (l) FIG. 1 (l) FIG. 1 (l) FIG. 1 (l) FIG. 1 (l) Number of islands [pieces] 18 18 18 18 18 18 Disposition of islands [circles] 3 3 3 3 3 3 Fiber Fineness [dtex] 66 66 84 84 84 100 properties Strength [cN/dtex] 2.3 2.1 3.5 3.0 2.6 2.7 Elongation percentage [%] 37 39 38 37 38 37 Extrapolated melting onset 233 185 236 236 236 236 temperature [° C.] Diameter R of fiber [nm] 9215 9169 17965 12707 10373 11320 Thickness T of outermost layer [nm] 1047 1032 1855 1368 1152 1187 T/R 0.114 0.113 0.103 0.108 0.111 0.105 Diameter r of island component [nm] 1159 1084 2320 1639 1341 1467 Diameter r1 of island component [nm] 1198 1043 2287 1676 1379 1455 Diameter r2 of island component [nm] 1157 1086 2322 1637 1339 1468 r1/r2 1.04 0.96 0.98 1.02 1.03 0.99 Fabric Moisture absorption rate difference 3.1 3.8 3.3 3.2 3.1 3.2 properties after scouring (ΔMR) [%] Moisture absorption rate difference 3.0 3.7 3.2 3.1 3.0 3.1 after hot water treatment (ΔMR) [%] Cracks of sea component [places] 3 2 0 1 2 2 L* value 21 24 20 21 23 22 Leveling S S S S S S Quality S S S S S S Dry touch S S S S S S PET: polyethylene terephthalate, PEG: polyethylene glycol, PBT: polybutylene terephthalate

TABLE 8 Comparative Comparative Comparative Example 6 Example 7 Example 8 Production Sea Polymer type Polyether Polyether Copolymerized conditions component ester ester PET Polyether type PEG PEG — Number average molecular weight of polyether [g/mol] 8300 8300 — Copolymerization ratio of polyether [% by weight] 30 30 — Moisture absorption rate difference (ΔMR) [%] 11.0 11.0 0.2 Extrapolated melting onset temperature [° C.] 236 236 233 Island Polymer type — PET PET component Polyether type — — — Number average molecular weight of polyether [g/mol] — — — Copolymerization ratio of polyether [% by weight] — — — Moisture absorption rate difference (ΔMR) [%] — 0.1 0.1 Extrapolated melting onset temperature [° C.] — 239 239 Sea/Island composite ratio [weight ratio] 100/0 30/70 70/30 Cross-sectional shape — FIG. 1 (1) FIG. 1 (1) Number of islands [pieces] — 18 18 Disposition of islands [circles] — 3 3 Fiber Fineness [dtex] 66 66 66 properties Strength [cN/dtex] 0.9 1.6 3.4 Elongation percentage [%] 21 24 35 Extrapolated melting onset temperature [° C.] 236 236 233 Diameter R of fiber [nm] 9051 9196 9248 Thickness T of outermost layer [nm] — 932 1089 T/R — 0.101 0.118 Diameter r of island component [nm] — 1825 1065 Diameter r1 of island component [nm] — 1868 1095 Diameter r2 of island component [nm] — 1822 1063 r1/r2 — 1.02 1.03 Fabric Moisture absorption rate difference after scouring (ΔMR) [%] 11.0 3.3 0.1 properties Moisture absorption rate difference after hot water treatment (ΔMR) [%] 10.7 3.0 0.1 Cracks of sea component [places] — 0 0 L* value 20 21 18 Leveling C B S Quality C B S Dry touch C C S PET: polyethylene terephthalate, PEG: polyethylene glycol

TABLE 9 Example 38 Example 39 Example 40 Example 41 Production Sea Polymer type PET PET PET PET conditions component Moisture absorption rate difference (ΔMR) [%] 0.1 0.1 0.1 0.1 Extrapolated melting onset temperature [° C.] 239 239 239 239 Island Polymer type Polyether Polyether Polyether Polyether component ester ester ester ester Polyether type PEG PEG PEG PEG Number average molecular weight of polyether [g/mol] 8300 8300 8300 8300 Copolymerization ratio of polyether [% by weight] 35 35 35 35 Alkylene oxide adduct m + n 4 6 10 30 of bisphenol Copolymerization ratio [% by weight] 19 16 14 14 Moisture absorption rate difference (ΔMR) [%] 11.5 11.2 11.0 13.3 Extrapolated melting onset temperature [° C.] 196 214 228 240 Sea/Island composite ratio [weight ratio] 70/30 70/30 70/30 70/30 Cross-sectional shape FIG. 1 (e) FIG. 1 (e) FIG. 1 (e) FIG. 1 (e) Number of islands [pieces] 24 24 24 24 Disposition of islands [circles] 3 3 3 3 Fiber Fineness [dtex] 66 66 66 66 properties Strength [cN/dtex] 2.9 2.8 2.6 2.3 Elongation percentage [%] 36 38 35 37 Extrapolated melting onset temperature [° C.] 196 214 228 239 Diameter R of fiber [nm] 9215 9349 9162 9204 Thickness T of outermost layer [nm] 997 1009 1034 1013 T/R 0.108 0.108 0.113 0.110 Diameter r of island component [nm] 1025 1041 986 975 Diameter r1 of island component [nm] — — — — Diameter r2 of island component [nm] 1025 1041 986 975 r1/r2 — — — — Fabric Moisture absorption rate difference after scouring (ΔMR) [%] 3.5 3.4 3.3 4.0 properties Moisture absorption rate difference after hot water treatment (ΔMR) [%] 3.4 3.3 3.2 3.8 Cracks of sea component [places] 3 2 2 4 L* value 24 24 25 26 Leveling S S S A Quality S S S S Dry touch S S S S PET: polyethylene terephthalate, PEG: polyethylene glycol

TABLE 10 Example 42 Example 43 Example 44 Example 45 Production Sea Polymer type PET PET PET PET conditions component Moisture absorption rate difference (ΔMR) [%] 0.1 0.1 0.1 0.1 Extrapolated melting onset temperature [° C.] 239 239 239 239 Island Polymer type Polyether Polyether Polyether Polyether component ester ester ester ester Polyether type PEG PEG PEG PEG Number average molecular weight of polyether [g/mol] 8300 8300 11000 20000 Copolymerization ratio of polyether [% by weight] 30 45 35 35 Alkylene oxide adduct m + n 10 10 4 4 of bisphenol Copolymerization ratio [% by weight] 14 14 19 19 Moisture absorption rate difference (ΔMR) [%] 8.9 18.6 12.0 12.5 Extrapolated melting onset temperature [° C.] 232 218 198 200 Sea/Island composite ratio [weight ratio] 70/30 70/30 70/30 70/30 Cross-sectional shape FIG. 1 (e) FIG. 1 (e) FIG. 1 (e) FIG. 1 (e) Number of islands [pieces] 24 24 24 24 Disposition of islands [circles] 3 3 3 3 Fiber Fineness [dtex] 66 66 66 66 properties Strength [cN/dtex] 2.9 2.3 2.8 2.9 Elongation percentage [%] 37 34 38 37 Extrapolated melting onset temperature [° C.] 232 218 198 200 Diameter R of fiber [nm] 9370 9136 9117 9281 Thickness T of outermost layer [nm] 1011 1005 1026 988 T/R 0.108 0.110 0.113 0.106 Diameter r of island component [nm] 1013 992 1037 1004 Diameter r1 of island component [nm] — — — — Diameter r2 of island component [nm] 1013 992 1037 1004 r1/r2 — — — — Fabric Moisture absorption rate difference after scouring (ΔMR) [%] 2.7 5.6 3.6 3.8 properties Moisture absorption rate difference after hot water treatment (ΔMR) [%] 2.6 5.4 3.5 3.7 Cracks of sea component [places] 1 4 3 3 L* value 24 28 24 24 Leveling S A S S Quality S A S S Dry touch S S S S PET: polyethylene terephthalate, PEG: polyethylene glycol

INDUSTRIAL APPLICABILITY

The sea-islands type composite fiber does not undergo the cracks of a sea component upon the volume expansion of a polymer having moisture absorbability that serves as an island component during a hot water treatment such as a dyeing treatment, thus rarely undergoes the generation of dyeing specks and/or fluffs when the composite fiber is formed into a fiber structure such as a woven fabric or a knitted fabric, and has excellent quality. In addition, the fiber is reduced in the elution of the polymer having moisture absorbability, thus has excellent moisture absorbability even after a hot water treatment, and also has dry touch inherent to a polyester fiber when the sea component is a polyester. Therefore, it can be suitably used as fiber structures such as a woven fabric, a knitted fabric, and a nonwoven fabric for clothing. 

1.-17. (canceled)
 18. A sea-islands type composite fiber comprising: an island component that is a polymer having moisture absorbability; a ratio (T/R) of a thickness T of an outermost layer to a diameter R of the fiber in a transverse cross section of the fiber of 0.05 to 0.25; and a moisture absorption rate difference (ΔMR) after a hot water treatment of 2.0 to 10.0%, wherein the thickness of an outermost layer is a difference between a radius of the fiber and a radius of a circumscribed circle formed by connecting apexes of the island components disposed in an outermost circle, and represents a thickness of a sea component in the outermost layer.
 19. The sea-islands type composite fiber according to claim 18, wherein the thickness T of an outermost layer is 500 to 3,000 nm.
 20. The sea-islands type composite fiber according to claim 18, wherein the island component has a diameter r of 10 to 5,000 nm in the transverse cross section of the fiber.
 21. The sea-islands type composite fiber according to claim 18, wherein the island component is disposed to 2 to 100 circles in the transverse cross section of the fiber.
 22. The sea-islands type composite fiber according to claim 18, comprising a ratio (r1/r2) of a diameter r1 of the island component disposed to pass through a center of the transverse cross section of the fiber to a diameter r2 of other island components of 1.1 to 10.0.
 23. The sea-islands type composite fiber according to claim 18, wherein a shape of a center side of the island component disposed in an outermost circle in the transverse cross section of the fiber is non-circular.
 24. The sea-islands type composite fiber according to claim 18, comprising a composite ratio (a weight ratio) of the sea component/the island component of 50/50 to 90/10.
 25. The sea-islands type composite fiber according to claim 18, wherein the polymer having moisture absorbability is at least one polymer selected from the group consisting of a polyetherester, a polyether amide, and a polyetherester amide containing a polyether as a copolymerization component.
 26. The sea-islands type composite fiber according to claim 25, wherein the polyether is at least one polyether selected from the group consisting of polyethylene glycol, polypropylene glycol, and polybutylene glycol.
 27. The sea-islands type composite fiber according to claim 25, wherein the polyether has a number average molecular weight of 2,000 to 30,000 g/mol.
 28. The sea-islands type composite fiber according to claim 25, wherein a copolymerization ratio of the polyether is 10 to 60% by weight.
 29. The sea-islands type composite fiber according to claim 25, wherein the polyetherester contains an aromatic dicarboxylic acid and an aliphatic diol as main components, and contains the polyether as a copolymerization component.
 30. The sea-islands type composite fiber according to claim 25, wherein the polyetherester contains an aromatic dicarboxylic acid and an aliphatic diol as main components, and contains the polyether and an alkylene oxide adduct of a bisphenol represented by Formula (1) below as copolymerization components:

wherein m and n are integers of 2 to 20 and m+n is 4 to
 30. 31. The sea-islands type composite fiber according to claim 29, wherein the aliphatic diol is 1,4-butanediol.
 32. The sea-islands type composite fiber according to claim 18, wherein the sea component is a cation dyeable polyester.
 33. A false twist yarn comprising a twist of two or more of the sea-islands type composite fiber according to claim
 18. 34. A fiber structure comprising the sea-islands type composite fiber according to claim 18 in at least a part of the fiber structure.
 35. A fiber structure comprising the false twist yarn according to claim 33 in at least a part of the fiber structure. 